Not much is known about Tommy Shepherd's history, save that his parents, Frank and Mary, are divorced. When the Young Avenger Hulkling was kidnapped by Kl'rt the Super Skrull, the Young Avengers needed more members in order to rescue Hulkling. Thomas Shepherd was listed in the Avengers Fail-Safe program as a possible Young Avenger. Tommy, however, was locked in a high powered juvenile hall facility due to him "accidentally" vaporizing his school. After releasing him, the team was shocked to find that Tommy and Wiccan bore an twin-like resemblance to one another. Tommy revealed that he had been locked up for months and during that time the facility's faculty had tried to turn him into a living weapon. He attacked the security guards and the fleeing doctors in an attempt at revenge. Hawkeye and Patriot managed to subdue Tommy and convince him to join the team in rescuing their teammate from the Super-Skrull.
After rescuing Hulkling, Tommy learned from the Super-Skrull that he and Wiccan could be the lost children of the Scarlet Witch. The Vision stated that the Scarlet Witch was so desperate to have children with her android husband, she used her reality-altering powers to create twin boys from two lost souls. Wanda and Vision named their children Thomas and William. Together they tried to live normal lives, until Mephisto claimed the two souls as his own. However, the souls were affected by Wanda's magic and destroyed Mephisto. Wiccan immediately accepted the idea that he was one of the Scarlet Witch's children, theorizing that when the souls destroyed and dispersed from Mephisto, the souls inhabited his and Tommy's bodies. Tommy however, was more skeptical about the idea.
After the Young Avengers helped stop the Kree and the Skrulls from declaring Earth their battleground for a second time, Tommy decided to officially join the team and took the codename of Speed.
With Wiccan, Speed went on a search for the Scarlet Witch. At that point, Speed's skepticism at being the Scarlet Witch's son seemingly diminished, as he openly called Wanda 'mom' and repeatedly referred to Wiccan as his brother. They searched Genosha and Wundagore before finding Master Pandemonium in New Jersey at the former residence of the Scarlet Witch and the Vision. There, Master Pandemonium urged both boys to embrace their present, as their past was nothing but chaos and darkness. Later, Speed and Hawkeye went on a date after she lost her codename and bow to Clint Barton. He also helped her break into the Secret Avengers' base so she could steal back the bow. The two kissed, but Kate decided to pursue a relationship with Patriot instead.
Speed joined the other Young Avengers in their attempt to convince the Runaways to join the Anti-Registration side. There, he developed a sibling-like bond with Molly Hayes.
The Young Avengers were one of the first teams to respond to the Skrull Invasion in New York. Speed and Wiccan saved Hulkling and Xavin from three attacking Skrulls and teamed up with the rest of the Runaways to stop an assassination attempt on Hulkling.
Speed was turned to stone, along with several other members of the Young Avengers. He and the others were freed thanks to the Mighty Avengers. When the Young Masters surfaced, Speed went with the rest of his team to confront them about using the name 'Young Avengers.' He was surprised to see Coat of Arms, a girl he met during his time in juvenile hall, and with whom he had an implied relationship. Speed offered her a place on his team of Young Avengers, as she did to him, but both opted to stay with their own teams.
Speed and the rest of the Young Avengers assisted Steve Rogers against Norman Osborn's Dark Avengers following the attack on Asgard. He delivered the suitcase containing the Iron Man armor to Tony Stark.
Avengers: The Children's Crusade
Speed accompanies the rest of the Young Avengers in the search for the Scarlet Witch. Magneto travels to Transia with the team. There he meet his uncle, Quicksilver, for the first time. They meet a Doombot Scarlet Witch, which leads Wiccan to teleport to Latveria. There he meet a Scarlet Witch that is engaged with Doctor Doom. The rest of the team and Magneto and Quicksilver follows him, and a battle begins between them and the Avengers against the Doombots of Latveria. The battle is interrupted by the arrival of Iron Lad.
The team and Scarlet Witch is travelling through the timestream to the time when Jack of Hearts returned and killed Scott Lang by exploding. However, they disrupt the scene and takes Scott with them to the present. Scarlet Witch regains her memory and realizes that Tommy and Billy is her sons.
Speed is with the team when they battle Doctor Doom who is powered with the life force. He would use the power to create a utopia he would rule. He is defeated by the Avengers and the X-Men but in the process Cassie is killed.
Iron Lad wanted to save Cassie by taking her into the timestream but Vision refused. This leads to Iron Lad destroying Vision and leaving into the future (this being the time when he becomes Kang the Conquerer.
After this, Speed is awarded the title of a full fledged Avenger together with the rest of the team. On Wiccan's request, the team disbands.
Young Avengers again
When Wiccan tries to bring back Hulkling's mother, he accidentally summons a dimensional creature known as Mother who takes control of the team's parents. During this time, Speed (who is no longer with the team) has been hired by a company that hires superhumans. His job is to assemble electronic devices that takes months for a normal person but a few minutes for him. He meets the former X-Man Prodigy (David Alleyne) who also works a the company, and together they are hunting down a thief wearing the costume of former Young Avenger Patriot. Speed is kidnapped by the interdimensional thief into other dimensions. Prodigy apprehends the Young Avengers to help him look for Speed. He and Prodigy engage in a short and brief relationship after Prodigy reveals himself as bisexual.
Powers and Abilities
Speed is superhumanly fast. Although his top speed is unknown, he can exceed the speed of sound (about 1,225 km/h, or 761 mph) and resist the effects of friction, reduced oxygen, and kinetic impact while moving at those speeds. He can also generate hyperkinetic vibrations that accelerate the molecules in matter, causing any solid object he directs his vibrations at to explode. In Young Avengers Presents #3 he asserts that he is "Quicksilver fast", shown running from the eastern seaboard of the United States to Genosha, an island off the east coast of Africa, as well as search the entire island for anyone living there in the same amount of time it takes Wiccan to teleport the same distance. This indicates that Speed is fast enough to run across the surface tension of a body of water without sinking. In addition, his mind can operate in an accelerated state, allowing him to read in super speed and remember everything he's seen. During the Civil War: Young Avengers and Runaways crossover, when both teams invaded the Cube in order to save their friends, Speed is shown exploding a gun in his hand by using his hyperkinetic vibrations. He is also able to accelerate his molecules (or even those of small groups of people) and vibrate fast enough to pass through solid matter, such as walls.
Avengers: The Crossing
Some readers speculated that the twins Malachi and Tobias were in fact the kidnapped children of the Scarlet Witch and the Vision. Thomas was believed to be Tobias, who attacked the Avengers with his brother during the Crossing story arc.
In one of the many dark possible futures unveiled to Immortus by The Time Keepers, Thomas and William were adults who wielded God-like powers that far surpassed their mother's. They were both seen launching a devastating assault on the abstract being known as Eternity, implying that they planned to overthrow him.
Avengers: Fairy Tales
In an Alice In Wonderland inspired reality, Speed played the part of the White Rabbit to Stature's Alice. He maintains his super-speed, as well as his connection to Wiccan, who took the part of the March Hare.
The Last Avengers Story
In the one-shot about the final battle of the Avengers, Tommy Maximoff became the disciple of Doctor Strange. In this reality, both he and Billy were raised as the children of Scarlet Witch and the Vision and witnessed the accidental murder of his mother by his uncle, Quicksilver. Wanda's death caused the Vision to retreat from humanity, and Tommy decided to become Strange's student. He attempted to convince his father to return to humanity and assist the Avengers in their final stand, but to no avail. Tommy joined the Avengers in their battle against Ultron, Kang and his own brother, the Grim Reaper. The brothers fought each other until their father intercepted and destroyed Ultron, thus ending the battle. Unlike his mainstream counterpart, this version of Tommy inherited his mother's reality-altering powers and mystical abilities, rather than the super-speed of his uncle.
In other media
Tommy is one of Wanda and Vision's twin boys with similar powers to his uncle Quicksilver. He is portrayed by Jett Klyne in WandaVision, the Disney+ streaming service.