From William the Bastard to William the Conqueror: The King Who Transformed England

William was born around 1027 in the town of Falaise in the Normandy region of France. His parents were Duke Robert I of Normandy and a woman named Herleve (or sometimes Arlette), the daughter of a tanner.

Robert and Herleve weren't married, but they weren't exactly illicit lovers, either. According to David Bates, author of the Yale University Press biography "William the Conqueror," Herleve was Robert's long-time "concubine" and partner, a relationship that wasn't uncommon in 11th-century France.

"What constituted a 'Christian marriage' wasn't actually made clear in canon law until the early 13th century," says Bates. "[Robert and Herleve's relationship] was a bit unusual, but not dramatically so."

What's clear is that Robert, who didn't have any other children, saw William as his legitimate heir, an unusual step at the time. And when Robert died during a pilgrimage to Jerusalem, 8-year-old William became Duke of Normandy. The young Duke's enemies, who tried unsuccessfully to steal his land and title, insultingly called him "William the Bastard."

By the time William was in his early 20s, he had quashed several internal rebellions and even captured neighboring territories. As Duke of Normandy, "he had a very strong reputation as someone not to mess with," says Hugh Thomas, history professor at the University of Miami and author of "The Norman Conquest: England After William the Conqueror."

As proof of William's fame as a formidable fighter and political leader, he had no trouble recruiting thousands of men from Normandy and Northern France to sail with him on an incredibly risky venture — the 1066 invasion of England to claim its throne for the Normans.

Norman means "men from the north" and that's exactly who they were — Viking invaders who settled in Northern France in the 900s C.E. Over time, they converted to Christianity and started speaking French, but they "continued to think of themselves as a distinct group," says Thomas.

England, meanwhile, had been ruled by Anglo-Saxon kings since the first Germanic tribes conquered the land known today as England in the fifth and sixth centuries C.E. The Anglo-Saxons spoke Old English and lived in "shires" ruled by aristocratic lords loyal to the king.

According to William, he was hand-picked to become the next king of England by Edward the Confessor, who died without an heir in 1066. But William wasn't the only pretender to the throne.

"It would have made for a good soap opera," says Bates, listing the various distant relatives who claimed they were the rightful heirs, including Harold Godwinson (a member of a powerful family), who said that Edward had chosen him as successor on the late king's deathbed.

"Since Edward was childless, everyone knew some terrible crisis was going to come," says Bates. "They had an awful long time to prepare without knowing exactly what form it was going to take."

Harold was crowned king on Jan. 6, 1066, but his reign would last just nine months and end with his death by a Norman sword.

The Norman invasion of England wasn't a rash attack. William took seven months to plan his campaign, eventually transporting 7,000 men and an estimated 3,000 horses across the English Channel on 600 Viking-style long boats.

William's timing, it turned out, was perfect. His nemesis, now dubbed King Harold II, was distracted by a Norwegian invasion of Northern England, allowing the Normans to land unchallenged in Southern England. After Harold fought off the Norwegians, he marched his battle-weary soldiers straight to Hastings, where William's veteran cavalry and archers sat waiting.

"It was a long and hard-fought battle, and a skillfully fought victory for William," says Bates.

The English, who had the upper ground, formed a shield line and repelled countless uphill attacks by the Norman cavalry. William himself had three horses killed under him. When a rumor spread that William was dead, he famously took off his helmet and rode through the ranks to rally his troops, a scene captured in the historic Bayeux Tapestry.

In a brilliant move, the Normans feigned retreat, which tricked some of the less-experienced English soldiers to break ranks and expose holes in their defense.

"It's not very bright," says Thomas, "chasing on foot people who are on horseback."

The Normans circled back and broke through the English line, killing Harold and his two brothers. The king-less English scattered in a panic and the grueling, day-long Battle of Hastings went to William, who was crowned King of England on Christmas Day, 1066.

As expected, Harold's supporters didn't roll over and accept William the Conqueror as their king. During the first years of William's reign, his enemies mounted numerous rebellions and uprisings, but none as sustained as those in Northern England centered around the shire of York.

To put an end to the fighting, William resorted to a scorched-earth tactic called "harrying" that was well-known in medieval times, but perhaps never executed with such severity. To "harry" is to burn and destroy the land and its resources so completely that nothing is left to sustain a rebellion. According to one 12th-century chronicler, as many as 100,000 peasants died from the famine that followed William's decimation of the north.

"This episode shows William being capable of extreme violence to achieve his ends," says Bates. "It's his ruthlessness taken to extremes."

When William took the throne, he left much of the Anglo-Saxon government in place, since it already had a sophisticated bureaucracy that included coinage and taxation. But he eventually took the dramatic step of dispossessing most of the Anglo-Saxon nobles and handing their lands over to loyal Norman elites.

Latin became the official language of English government, explains Thomas, because it was a language that both English and Norman bureaucrats could understand. While the lower social classes continued to speak Old English, the English elites and their hangers-on started speaking French, and it remained the language of the upper classes well into the 13th century, says Bates.

As a result of the Norman invasion, modern English contains roughly 10,000 French words, and an estimated 58 percent of English words are derived from French or Latin. Interestingly, William spoke no English and was illiterate, like many noblemen of the day.

Once William installed loyal Norman subjects as feudal lords, he wanted to determine exactly how many resources were under his control. So, he ordered a nationwide survey of every shire, farm, shop and household down to the number of sheep in the yard and bushels of grain in the storehouse.

"It's this massive undertaking by the standards of the time," says Thomas. "The local people compared it to the Last Judgement, when every single sin and good deed would be counted."

When this huge collection of demographic and economic information was published, it was dubbed the Domesday Book, pronounced "doomsday." To this day, historians covet the reams of 12th-century data captured by this wildly ambitious survey.

"There's nothing else before or after that survives like that," says Thomas. "It's this incredible snapshot of England's economy."

Despite being King of England, William mostly ruled from Normandy, where he was also besieged by rebellions. In 1087, a year after the completion of the Domesday Book, William fell from a horse while attacking the French city of Mantes and died from his injuries.

He was buried in the Abbey of St. Stephen in Caen, France, a building that William constructed in 1077 as a favor of sorts to the Church. Pope Leo IX had opposed William's marriage to his close cousin Matilda in 1050, but William promised to build a pair of abbeys in Caen if the Pope agreed to bless the union, which he did.

A simple stone laid in the abbey is etched with this epitaph: "Here lies the invincible William the Conqueror, Duke of Normandy and King of England."

William and Matilda had 10 children, including William II, who succeeded his father as King of England. The current Royal Family of the United Kingdom is related to William by way of a complicated and twisting pedigree. There have been four English kings named William and will likely be a fifth if Prince William assumes the throne as expected.