William and Mark have been friends long before Mark developed his powers in their senior year. William prefers to be called by his full name William and immensly dislikes it when people try to shorten his name with nicknames like Bill, billy or Will.
At one point in an orientation visit to their new college, Upstate University, one of D.A. Sinclair's Reanimenwent on a rampage through the college grounds. After making sure William was safe, Mark disappeared and Invincible arrived to fight a short brawl with the Reaniman. At the battel's conclusion, William nonchalantly asked Mark when he was going to let him know he had gotten super powers.
William reassured Mark his secret would be safe, and soon after imposing on his best friend to take him flying. William was good to his word and kept the secret safe, even though the superhero life and Mark's new girlfriend limited their "hanging out " time.
When Mark was seriously injured during a fight with his father, Omni-Man, William's concern for his friend became evident. When Mark returned as best he could to a normal life, William was there to support and stick up for him. It was during this time that William and Atom Eve started a short-lived relationship.
When the school year started, Mark and William became dorm-mates. William remained compassionate of Mark and his family concerns, and counseled him on the girl problems his life as Invincible caused. Unfortunately, William and Mark's relationship has been increasingly strained as super-heroics, girlfriends and schoolwork take more "buddy" time away from them. When their college friend Rick Sheridan disappeared, William snapped at Mark over his lack of action regarding the matter. Though their friendship was rocky, the two still remained roommates and friends. William later goes on to share a room with Rick instead of Mark. After Mark returns from his multi-month journey it is revealed that Rick and William are partners and that William is gay.
William possesses the normal human strength of a man his age, height and build who engages in regular exercise.
Known superhuman powers: None