William Harrison is the protagonist of the Weird William series.
William has uncombed black hair. He has a black shirt with the first letter of his name on it. He wears blue jeans with red sneakers. The Omnitrix II is on his left wrist.
William is a brave and determined young lad, who always craves for adventure. He enjoys teasing Calvin and will always help anyone in danger, meaning that he is a social server. He is also ready to risk his life, as he decides to sacrifice himself instead of Ben, and only leaves the 'Ultimate Null Void', after constant persuasion from Ben.
In 2035, William and his parents moved from Cherry Valley to Bellwood, when his father got a big job there. William was a sincere fan of Ben Tennyson, and only stopped wearing his Ben 10 shirt,when he was a kid, when his mom threw it away. He had lots of Ben 10 collectibles, from Ben 10 watches to Ben 10 action figures. To his disappointment, there was a rumor that Ben Tennyson was missing in Bellwood City, even though his grandfather lived next door. One day, after being bullied by his new classmates at school, a gloomy William was walking towards his house, when he overheard Max Tennyson talking with Gwen and Kevin about the truth about Ben, which was that Ben was on a mission to destroy a deadly enemy in a modified Null Void called the 'Ultimate Null Void' (the one Grandpa had was the only one) to seal the enemy there forever. When the trio leave the house for a walk, Will steals the 'Ultimate Null Void Projector', and goes inside the void. There, he gets attacked by alien beasts, and Ben himself, as Omni Alien, defeats the beasts. Then the duo travel across the Ultimate Null Void, defeating monsters and finding paths, until they come across the enemy, Nemesis. Nemesis proved to be a major threat and both of them would have died, if Ben hadn't transformed into Ultimate Alien X and saved them. Ben as Ultimate Alien X, gives William the Omnitrix II, telling to him that it was specially made for himself, but since he was about to die (by sealing the void, all the organisms inside it dies), he gives the Omnitrix II to Will and seals the place, with William escaping as Shadow Face. Finally, Will learns how to master the new Omnitrix.
Meanwhile, a shadowy form appears in a misty planet, looks at a portal where the Tennysons are happy after a long time and says with a genderless voice, that its henchman had died, that the Tennysons had mistaken him as the enemy, and that the real enemy was right here.
- William is the hero continuing Ben's duty.
- He is a major fan of Ben.
- The Omnitrix II is far more enhanced than the other Omnitrix.