Years ago during a battle with the Salem Seven, the Scarlet Witch (Wanda Maximoff) channeled the chaos magic found within New Salem, inadvertently using fragmented energies of the Hell-lord Mephisto, into herself to conceive twin sons. Believing the twins were fragments of his own lost soul, Master Pandemonium abducted the twins resulting in the twins seemingly being reabsorbed into a reconstituted Mephisto; however, the twins' souls had been so transfigured by the Scarlet Witch's magic that they temporarily destroyed Mephisto. Believed destroyed, the twins' souls were apparently cast back in time & reborn as individual entities. Thomas ended up in Springfield, new Jersey, while William was adopted by Jeff & Rebecca Kaplan & raised in New York's Upper West Side by Frank & Mary Sheperd.
Often erupting into violent behaviors, Thomas was arrested & placed in the NJ Youth Correctional Facility after "accidentally" vaporizing his school where they attempted to turn him into a weapon. When the Hulkling (Teddy Altman) was abducted by the Super-Skrull (Kl'rt), the Vision used the Avenger's fail-safe program to locate Thomas to recruit him into the Young Avengers. Upon being rescued, the Young Avengers discovered Thomas & Wiccan (William Kaplan) looked nearly identical & Wiccan later came to believe the two were both sons of the Scarlet Witch. After rescuing Hulkling & narrowly averting a war between the interstellar Skrull & Kree Empires, which both claimed custody over Hulkling, Wiccan & Thomas, now calling himself "Speed," planned to locate their missing mother; but they were interrupted when the SHRA (Superhuman Registration Act) passed & the Young Avengers were banned as outlaws when they failed to register. Captured by a SHIELD Superhuman Restraint Unit, the Young Avengers were soon rescued by Captain America (Steve Rogers) & joined his underground resistance movement. Afterward, the Young Avengers helped the young Runaways team escape a similar arrest by SHIELD & teamed up against Marvel Boy (Noh-Varr), a nanite-controlled agent of the top-secret Cube prison facility. Speed was among the heroes captured by the Cube's Warden, although he was promptly rescued by the Young Avengers & Runaways who had not been apprehended.
When the Skrulls began their invasion of Earth, the Young Avengers joined in stopping their plans of world domination. Afterward, Speed & Wiccan traveled to Genosha, Wundagore Mountain, & the Cresskill house, searching for answers to questions about their origins. Strangely, it was Master Pandemonium helped the twins realize they should embrace the present & not the horrid past they once lived.