William Colter is a character in the Once Upon a Time graphic novel, "Out of the Past". He is the brother of Queen Regina's former lover, Daniel, and also an accomplice of the thief, Jefferson. After years of thievery with the portal-jumper, William met his demise during a run-in with Regina where he attempted to kill her, blaming her for his brother's death. Though he tried, he failed when the Queen reluctantly used magic to end his life in order to save her own.
Before the Curse
When his brother Daniel was still a child, William left the family to seek fortunes in a faraway realm. At one point, he begins stealing treasures with an accomplice, Jefferson, and later learns that Daniel has since died at the hands of his love's mother. Blaming Regina for his brother's death, he makes plans to return to the Enchanted Forest and exact revenge. Before he does, however, William learns that the March Hare of Wonderland now has the Clock of Evermore, giving him the ability to manipulate time. With the more pressing matter of finding Regina, he decides against pursuing the relic and instead sends Jefferson a letter about the clock's whereabouts. From an unnamed realm, William gains magic sand from a sea nymph so he can neutralize Regina's powers. While Regina's carriage is traveling through the Forest of the Dead, William causes it to flip, before luring the Queen into falling into his pit trap. She denies killing Daniel, instead continuing to blame Snow White for instigating her lover's demise, but William believes a romance between a peasant and noble was doomed from the beginning. As he begins sprinkling the sand on her, she counters with magic, accidentally delivering a fatal death blow to him. Not meaning to have hurt him, Regina asks him to hold on as she heals him, but William states she won't be able to just as she couldn't save Daniel. ("Out of the Past")