Speed

The Young Avengers found Tommy Shepherd in a juvenile detention facility for superhuman minors, locked up for blowing up his high school. He was Billy Kaplan's face with none of Billy's caution: fast, cocky and completely uninterested in being anybody's redemption story. Then they discovered they were twins, and that both of them are the reincarnated souls of the children Wanda Maximoff conjured and lost.

That makes Tommy the brother of Wiccan, the nephew of Quicksilver, and a walking argument about whether the Maximoff family is capable of producing anyone stable. He is the team's fastest member, its most reliable source of bad decisions, and, in the rare quiet moments, the one who most obviously wants a family and least knows how to ask.

Heinberg and Cheung introduced Tommy in Young Avengers #10, and the reveal that he was Billy Kaplan's twin reframed the whole run. He became a fixture across Avengers: The Children's Crusade, Avengers Academy and the various Young Avengers revivals, usually as the member most likely to make a crisis worse before making it better.

The MCU seeded him in WandaVision as Tommy Maximoff, one of Wanda's hex-born twins, and Agatha All Along has continued threading the reincarnation logic that the comics established.