William was conceived in 2007 following Oliver Queen's affair with Samantha Clayton. Oliver shared the news with his mother, Moira, expressing that he had messed up. Thinking this could potentially ruin Oliver's life, Moira paid the girl one million dollars to pretend she had miscarried and "asked" her to move away to Central City and never to see Oliver again.
Almost 8 years later, William's mother visited CC Jitters. She called him, promising to be back with a hot chocolate soon.
Many months later, William was running through CC Jitters with his action figure and ran into his father, Oliver, unbeknownst to both of them. Oliver gave William back his figure, which he'd dropped, and he ran to his mother.
On his way to a sporting event, William and his mother were briefly stopped by Oliver. While his mother was conversing with Oliver, William told her mother to hurry or they'd miss the game.
Later, while playing with his action figures on the patio, he and his mother were interrupted by Oliver once again. He was then told to go play with his toys inside the house.
The following day, William was formally greeted by Oliver, who told him he was an old friend of his mother's. He was asked if it was okay if he visited him once in a while and the two played with his Flash and Captain Cold action figures.
Darhk later kidnapped William, and brought him to his home to be his daughter's playmate. But its later revealed that he was taken by Malcolm Merlyn.
He was rescued by Team Arrow and admitted to his mother at the SCPD that he was bored with his Flash action figure and now wanted one of the Green Arrow. After that Oliver sent him and his mother away to keep them safe, also making a recording that was meant for William to hear on his eighteenth birthday, revealing their relation and his identity as the Green Arrow to his son.
- William's aunt Thea and his step-mother Nyssa are both illegitimate children just like him. All three are also children to men that held the title of Ra's al Ghul.
- His father was Ra's al Ghul for a short time, he would possibly have been Heir to the Demon like Maddox, Thea and Nyssa.
- William is a fan of the Flash, as he is seen with a few of his action figures, including posters from Flash Day in his room. Ironic as his father is Green Arrow, a good friend of the Flash.
- After being saved from Damien Darhk by the Green Arrow he states he is over the Flash.
- In a currently erased timeline William, along with everyone in Central City, was killed by Vandal Savage using the Staff of Horus in his efforts to kill Carter Hall and Kendra Saunders. However due to Barry Allen changing the time continuum this disaster never occurs.
- According to Malcolm Merlyn, William is the person that Oliver loves and cares about most in the world, even more than Thea and Felicity.