William Corvinus is the first Lycan Elder in the Underworld mythos, later followed by Lucian. He is the son of the first immortal and was bitten by a wolf, thus turning him into a Lycan (werewolf). He is played by Brian Steele.
William was the son of Alexander Corvinus and the twin brother of Marcus Corvinus. Both were born sometime in the 5th century. He, along with Marcus, inherited the genetic immortality strain from his father. This strain was created once the unique Corvinus blood type came into contact with a regional plague. The plague somehow altered the Corvinus blood type, causing the DNA to provide a form of immortality and strength. Marcus was eventually bitten by a bat and William by a wolf. The introduction of the new animal DNA caused each sibling to further mutate, thus William became the first true Werewolf. Unlike later werewolves known as Lycans, he was an albino werewolf and could not transform back to human form. His lycanthropy virus was much more infectious than Marcus' vampire virus, even allowing dead victims to transform.
In 1202, he was captured by Marcus' Death Dealers just after he infected an entire village. Against Marcus' wishes, William was imprisoned by Viktor in his fortress, far from Marcus' reach. This caused Marcus to swear vengeance against Viktor and those loyal to him.
Centuries later, William was freed from his dungeon by his brother, Marcus. Marcus and William both shared a bond that Alexander never truly saw. It was this remaining bond that caused William to recognize Marcus, even through his own bestial nature. William proved to be a powerful creature, despite his centuries of confinement with no food to feed on. He infected the Cleaners who came to fight him and also combated the hybrid Michael Corvin, descendant of his mortal brother, absorbing immense amounts of damage with no obvious signs of trauma done to him. The centuries of foodless confinement, however, still left William significantly weaker than he once was. Because of this, he was unable to defeat the powerful hybrid, Michael, who tore apart the Lycan Elder's head with his bare hands.