William was born c.1028;. He ruled as the Duke of Normandy from 1035 to 1087 and as King of England from 1066 to 1087.

Historically, as Duke of Normandy, he is known as William II, and, as King of England, as William I. He is commonly referred to as William the Conqueror (Guillaume le Conquérant) or William the Bastard (Guillaume le Bâtard). Several citizens taunted him during the siege of Alençon with reference to his illegitimacy and he had their eyes gouged out and their hands and feet cut off.

In support of his claim to the English crown, William invaded England in 1066, leading an army of Normans to victory over the Anglo-Saxon forces of Harold Godwinson at the Battle of Hastings, and suppressed subsequent English revolts in what has become known as the Norman Conquest

His reign brought Norman culture to England, which had an enormous impact on the subsequent course of England in the Middle Ages. In addition to political changes, his reign also saw changes to English law, a programme of building and fortification, changes in the English language and the introduction of continental European feudalism into England.

No authentic portrait of William has been found. Nonetheless, he was depicted, as a man of fair stature, with remarkably strong arms, "with which he could shoot a bow at full gallop". William showed a magnificent appearance, possessing a fierce countenance. He enjoyed an excellent health nevertheless his noticeable corpulence augmented eventually so much that the French king Philip I commented that William looked just like a pregnant woman. Also, William was hairless, about his forehead.

By his controversial birth, the enemies of William commented derisively that William was as stinking as a tanner shop, which was the low and noisome occupation of his mother's family. Nonetheless, William was enthusiastic for hunting so, after conquering England, many miles of land - 36 parishes - were seized by William, who expelled its inhabitants, becoming the royal New Forest region  for practicing this sport regularly.

William was born in Falaise, Normandy (northern France, nowadays), the illegitimate and only son of Robert II, Duke of Normandy, who named him for heir of Normandy. His mother, Herleva (among other names), who later had two sons to another father, was the daughter of Fulbert, most likely a local tanner. William's birth is believed to have been in either 1027 or 1028, and more likely in the autumn of the latter year. He was born the grandnephew of Queen Emma of Normandy, wife of King Ethelred the Unready and later of King Canute the Great.

By his father's will, William succeeded him as Duke of Normandy at the young age of seven in 1035 and was known as Duke William of Normandy (French: Guillaume, duc de Normandie; Latin: Guglielmus Dux Normanniae). By the reviling Norman noblemen, who had better claim for duke, the usual plots to usurp his place cost William, who was supported by the king Henry I of France, three guardians, though not Count Alan of Brittany, who was a later guardian. William was knighted by Henry at the age of 15. By the time he turned 19 he was successfully dealing with threats of rebellion and invasion. With the assistance of Henry, William finally secured control of Normandy by defeating rebel Norman barons at Caen in the Battle of Val-ès-Dunes in 1047, obtaining the Truce of God, which was backed by the church. Nonetheless, still, William was too weak, politically.

Against the wishes of Pope Leo IX, William married his cousin Matilda of Flanders, who resisted much the marriage by the half-bastard state of William, in 1053 in the Cathedral of Notre Dame at Eu, Normandy, Seine-Maritime. At the time, William was aged about 26 and Matilda aged 22. Whereas William was a faithful husband who cherished his wife for life, their marriage produced four sons and six daughters. In repentance for what was a consanguine marriage (as in "same blood"), William donated St-Stephen's church, l'Abbaye-aux-Hommes and Matilda donated Sainte-Trinité church, Abbaye aux Dames. However, King Henry became concerned because the noble marriage of William increased the power of the Normans too much. Consequently, Henry attempted invading Normandy twice in 1054 and 1057, to no avail though. William's half-brothers Odo of Bayeux and Robert, Count of Mortain played significant roles in his life. He also had a sister, Adelaide of Normandy, also through Robert and Herleva.

The principle children of William and Matilda were:

Robert 111 Curthose

Henry Beauclerc, King Henry 1

William believed that once the childless Edward the Confessor was dead, he would be the rightful king of England. Particularly, William argued his blood relatedness, linking himself to Emma, Ethelred's wife. It is probable that Edward, who was Robert II's cousin, had promised him the throne. William claimed that this had occurred, visiting London in 1052. Also, it is known that in 1064, the powerful earl of Wessex Harold Godwinson, who was an English paladin for the Saxon culture against the Normans, had pledged his allegiance to William. Confronting the count of Ponthieu, William had rescued Harold, who shipwrecked, and together they defeated Conan II, Count of Brittany, then. In that occasion, William knighted Harold and he pledged ceding his royal aspirations to William, who tricked him keeping some hidden saint's bones before him during the oath.

In any case, the vacancy of the English crown, which was left after Edward the Confessor died, would be ferociously disputed by three European figures - William, Harold, and the Viking king Harald III of Norway. In January 1066, by Edward's last will, Harold Godwinson was crowned King of England as Harold II, by the Witenagemot, and immediately, the new monarch raised a large fleet of ships and mobilized a force of militia, arranging these around the coasts, to anticipate attack from several directions.

The first would-be attacker was Tostig Godwinson, Harold's brother, but he was successfully defeated by Edwin, Earl of Mercia at a battle on the south bank of the Humber.

Meanwhile, William submitted his claim to the English throne to Pope Alexander II, who sent him a consecrated banner in support. Then, William organized a council of war, at Lillebonne and openly began assembling an army in Normandy, consisting of his own army, French mercenaries, and numerous foreign knights who expected plunder or English land. To each man, William promised both lands and titles of nobility, for after their victory. Despite gaining the support from many knights and gathering a considerable army of 600 ships and 7000 men at Saint-Valery-sur-Somme, due to the heavy militia presence on the south coast of England and the fleet of ships guarding the English Channel, it looked as if he might fare little better than Tostig.

However, once the harvest season arrived, Harold withdrew the militia on 8th September, due to falling morale and dwindling supplies, and consolidated the ships in London, leaving the channel unguarded. Then came the news that Harald III of Norway had landed ten miles from York with Tostig, which forced Harold and his army to head north. After a victory against the forces of earls Edwin of Mercia and Morcar of Northumbria at the Battle of Fulford, Harald and Tostig were defeated by Harold's army at the slaughterous Battle of Stamford Bridge on 25th September.

After weeks of unfavourable weather affected the English Channel, delaying William's departure but granting Harold, who moved out of the nearby English coasts, William arrived with his army in Pevensey Bay (Sussex) on 28th September and then he moved to Hastings, a few miles to the East, where he built a prefabricated wooden castle for a base of operations.

On 13th October, William received news that the already weakened army led by Harold was approaching from London, and at dawn the next day, William left the castle with his army and advanced towards the enemy, which was numerically similar and which had taken a defensive position atop the Senlac ridge, about seven miles from Hastings, at Battle town, nowadays. Harold disposed the English soldiers, over the route which connected to London

The Battle of Hastings lasted all of that day. Along the ridge's border, hiding behind a large wall of shields, all English soldiers stood so effectively that, initially, William's army couldn't even reach the high enemy, suffering a large number of casualties. However, to pursue the many fleeing Normans, many English soldiers broke their ranks so disorderly that William, whose horse had collapsed, could lead some Norman knights who were followed by the rest of the Normans, back into the battlefield. Thus, the battle was even while the English wall of shields weakened progressively, to disappearance. Then, William launched an effective wave of arrows over the shields, which decided the Norman victory irrevocably. This resulted in the deaths of Harold, who would have been killed by an arrow by a severe eye-wound, and two of his brothers, Gyrth and Leofwine Godwinson. At dusk, the English army made their last stand. By that night, the Norman victory was complete and the remaining English soldiers fled, in fear.

For two weeks, William waited for a formal surrender of the English throne but the Witenagemot proclaimed the quite young Edgar Ætheling instead, without coronation though. Thus, William's next target was London, approaching proudly through the important territories of Kent, via Dover and Canterbury, inspiring fear to the English. However, at London, William's advance was beaten back at London Bridge, deciding then to march westward and to storm London from the northwest. After receiving continental reinforcements, William crossed the Thames at the central-English town of Wallingford and there he forced the surrender of Archbishop Stigand, who was one of Edgar's lead supporters, in early December. William reached Berkhamsted a few days later where Ætheling relinquished the English crown personally and the exhausted Saxon noblemen of England surrendered definitively. Although William was acclaimed then as English King, he requested being crowned at London. As William I, he was formally crowned on Christmas Day 1066, in Westminster Abbey, by Archbishop Aldred.

Although the south of England submitted quickly to Norman rule, particularly in the North resistance continued for six more years until 1072. During the first two years, King William I suffered many revolts throughout England - in Dover, western Mercia, Wales and Exeter. Also, in 1068, Harold's illegitimate sons attempted an invasion of the southwestern peninsula but William defeated them.

However, against William I, the worst crisis came from Northumbria, which had not submitted to his realm still. In 1068, with Ætheling, both Mercia and Northumbria revolted. William could suppress these but Ætheling ended at Scotland where Malcolm protected him. Furthermore, Malcolm married Ætheling's sister Margaret, with much éclat, stressing the English balance of power against William. Under such circumstances, Northumbria rebelled, besieging York. Then, Ætheling resorted also to the Danes, who disembarked with a large fleet at Northumbria, claiming the English crown for their King Sweyn II. Besides, Scotland joined the rebellion, as well. Easily, the rebels captured York. However, William could contain them, at Lincoln. After dealing with a new wave of revolts in western Mercia, Exeter, Dorset and Somerset), William defeated his northern foes decisively at the Aire river, retrieving York, while the Danish army swore their departure.

Then, the revengeful William decided devastating Northumbria, between the Humber and Tees rivers, with his Harrying of the North. The region ended absolutely deprived, losing its traditional autonomy toward England. Then, the Danish king disembarked in person, readying his army to restart the war, but William suppressed such threat, with a payment of gold. Subsequently, in 1071, William defeated the last rebel focus of the north through an improvised pontoon, subduing the Ely island, at which the enemy had gathered. In 1072, he invaded Scotland, defeating Malcolm, who sought peace, which resulted just temporary. In 1074, Ætheling submitted definitively, to William.

In 1075, during William's absence, the last complication happened, by the Revolt of the Earls, which was confronted successfully by Odo. In 1080, William sent his half brothers Odo and Robert, who stormed Northumbria and Scotland, respectively. Eventually, the Pope protested against the excessive mistreatment, which had been exerted by the Normans, against the English people. Indeed, until overcoming all rebellions, William had conciliated with the English church although he persecuted it ferociously, afterward.

As it was usual among the Norman leaders, also William spent much time, 11 years, since 1072, off England, at Normandy, ruling the islands through his writs. Still as a vassal state nominally, owing its entire loyalty to the French King, Normandy arose suddenly though, as a powerful region, alarming the other French Dukes, which reacted attacking it persistently. Particularly, as Duke of Normandy, William was obsessed to conquer Brittany and the French King Philip I admonished him, against such ambition. Nonetheless, in 1086, William invaded Brittany, forcing the flight of the Duke Alan IV, nevertheless they agreed peace and William betrothed Constance, who ended poisoned few years later, to Alan.

Also, William dealt with some familiar issues. The mischief of his elder son Robert arose after a prank of his brothers William and Henry, who wetted him with filthy water. The situation became a large scale Norman rebellion and, only with King Philip's additional military support, William was able to confront Robert, who had based at Flanders. During the battle in 1079, William ended unhorsed and wounded by Robert, who lowered his sword only after recognizing him. The embarrassed William returned to Rouen, abandoning the expedition. Although, in 1080, Matilda reconciled both, William ended skimping Robert's inheritance. Also, with his usual misbehaviour, the unreliable Odo caused many troubles to William and he ended imprisoned in 1082, losing his English estate and all royal functions, except the religious ones. In 1083, Matilda died and the now bittersweet William became more tyrannical than ever, over his realm.

William initiated many major changes. He accented the function of the traditional English shires (autonomous administrative regions), which were centralized under his rule. Besides, all administrative divisions of his government remained immobile at determined English towns, so these strengthened progressively, along the years, and the English institutions ended amongst the most sophisticated in Europe. Accordingly, in 1085, in order to ascertain the extent of his new dominions and to improve taxation, William commissioned all his counsellors, for the compilation of the Domesday Book, which was published in 1086, a survey of England's productive capacity similar to a modern census.

Since early, William also ordered many castles, keeps, and mottes, among them the Tower of London's foundation (the White Tower), which were built throughout England. These ensured effectively that the many rebellions by the English people or his own followers did not succeed.

His conquest also led to Norman and French replacing English as the language of the ruling classes for nearly 300 years. Furthermore, the original Scandinavian cultural influence of England became mingled with the Norman one thus, beside the Anglo-Saxon culture, now the Anglo-Norman one came into being.

William is said to have eliminated the native aristocracy in as little as four years. Systematically, he despoiled those English aristocrats, either who opposed the Normans or who died without issue. Thus, most English estates and titles of nobility were handed to the Norman noblemen. Many English aristocrats fled to Flanders and Scotland, others may have been sold into slavery overseas. By 1070, the indigenous nobility had ceased to be an integral part of the English landscape, and by 1086, it maintained control of just 8 percent of its original land-holdings. However, to the new Norman noblemen, William handed the English parcels of land piecemeal, dispersing these wide, thus nobody would would conspiring against him, without jeopardizing their own estates, within the so unstable England. Effectively, this strengthened William's political stand, as a monarch.

In 1087, in France, William burned Mantes, which was 50 km westward from Paris, besieging the town subsequently. However, he fell off his horse, suffering fatal abdominal injuries, by the saddle pommel. In his deathbed, William divided his succession for his sons questionably

• Despite the reluctant William, the conflictive elder son Robert received the Normandy's dukedom, as Robert III in 1087.

• William Rufus, the third son, was next English king, as William II in 1087.

• William's youngest son Henry received 5000 silver pounds, which would be earmarked to buy land. He also became King Henry I of England, after William II died without issue.

Also during his deathbed, William pardoned many of his political adversaries, among whom Odo was one

William died at the age of 59, at the Convent of St Gervais, near Rouen, France, on 9th  September 1087. William was buried in the Abbaye-aux-Hommes, which had been erected by him, in Caen, Normandy.

According to some sources, a fire broke out during the funeral; the original owner of the land on which the church was built claimed he had not been paid yet, demanding 60 shillings, which William's son Henry had to pay on the spot; and, in a most unregal postmortem, William's now corpulent body would not fit in the stone sarcophagus. Whether or not it burst after some unsuccessful prodding by the assembled bishops, filling the chapel with a foul smell and dispersing the mourners is a matter of some speculation.

William's grave is currently marked by a marble slab with a Latin inscription, the slab dates from the early 19th century. The grave was defiled twice, once during the French Wars of Religion, when his bones were scattered across the town of Caen and again during the French Revolution. Following those events, only William's left femur remains in the tomb.