Speed can move, think and react at superhuman speeds. His entire body is adapted towards the rigors of high-speed running, including his cardiovascular and respiratory systems. He metabolizes an estimated 95% of caloric energy content of food (normal human use is about 25%). His enhanced musculature makes him virtually tireless due to his metabolism not producing fatigue-building poisons. His body constantly expels waste products during his accelerated respiration through exhalation. His tendons have the tensile strength of spring steel and his bones can withstand high-speed impacts because they are significantly more durable than normal calcium.
Speed’s practical reaction time is about five times faster than a normal human’s and the speed at which his brain processes information is heightened to a level commensurate with his bodily speed, enabling him to perceive his surroundings while traveling at high velocities. Speed’s body has an invisible aura that prevents his clothing from being affected by air friction as he moves at high speeds.
Speed can run at supersonic speeds, and is capable of short bursts of speed well beyond supersonic levels. At his average speed, he can run for about four hours until he needs to replenish his energy. He can run up vertical surfaces before gravity overtakes him and run across liquid by moving too fast to break its surface tension. By rapidly vibrating his hands in close proximity, Speed creates hyperkinetic vibrations he can direct at a target, accelerating and destabilizing its atomic matter until it explodes.
Years ago during a battle with the Salem's 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 and reborn as individual entities. Thomas ended up in Springfield, New Jersey, while William was adopted by Jeff and Rebecca Kaplan and raised in New York’s Upper West Side by Frank and Mary Shepherd.
Often erupting into violent behavior, Thomas was arrested and 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 Avengers’ fail-safe program to locate Thomas to recruit him into the Young Avengers. Upon being rescued, the Young Avengers discovered Thomas and Wiccan (William Kaplan) looked nearly identical and Wiccan later came to believe the two were both sons of the Scarlet Witch. After rescuing Hulkling and narrowly averting a war between the interstellar Skrull and Kree Empires, which both claimed custody over Hulkling, Wiccan and Thomas, now calling himself “Speed,” planned to locate their missing mother; but they were interrupted when the Superhuman Registration Act (SHRA) passed and 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) and joined his underground resistance movement, the "Secret Avengers." Afterward, the Young Avengers helped the young Runaways team escape similar arrest by SHIELD and 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 and Runaways who had not been apprehended.
When the Skrulls began an invasion of Earth, the Young Avengers joined in stopping their plans of world domina- tion. Afterward, Speed and Wiccan traveled to Genosha, Wundagore Mountain, and Cresskill, New Jersey in search of the Scarlet Witch, whom they believe to be their mother, but found Master Pandemonium, who sought to escape the life of the demonic being he had become, liv- ing in the Cresskill house. Master Pandemonium helped the twins realize they should embrace the present and not the horrid past they once lived . In the aftermath of the Skrull Invasion, the Young Avengers battled the Young Masters – Big Zero (Amity), Enchantress (Sylvie Lushton), Executioner (Danny), Melter (Christopher); Egghead (an android from the Microverse) and Coat of Arms, whom Thomas previously met years ago while in juvenile detention.