Helen Wheels

Helen Wheels is a Plumber's kid. She is the younger adopted sister of Pierce, as well as Manny's partner.

Personality
Helen is smart, brave, kind, nifty, and level-headed, though at times she usually tries to act rational and wise, making her mostly a mirror image of Gwen Tennyson, as well as an older sister figure for younger Plumbers such as Cooper and Alan. She is shown to be devoted to Max, willing to help him when he was seemingly attacked by Ben.

Helen shares a love-hate relationship with Manny. While Manny is usually hot-headed, aggressive and enjoys using violent methods, Helen is usually more careful and less aggressive, causing occasional arguments. On the other hand, she stated that they worked better teaming together than with other Plumbers, and shows true concern when seeing him injured or in danger.

Powers and Abilities
Being a Kineceleran hybrid, Helen possesses powers and appearance similar to XLR8: her feet end with wheel-like appendices, making her able to move like a roller skater and giving her incredible speed. How exactly fast she can go has not be revealed, but she's shown being able to move fast enough to do the same things as XLR8, such as racing up a wall or creating miniature tornadoes.

Helen has also learned how to use her speed to her own and her team's advantage beyond the obvious; during the climax of Above and Beyond, in conjunction with Alan, Helen helped to restrict Humungousaur's movements and range of vision by using the airflow produced by her super speed to fan Alan's flames.

In addition to her powers, Helen is shown to be quite skilled with computers and technology.

Prior to Alien Force
Helen was originally part of a small team of "Plumbers' helpers", young Plumbers' apprentices, with her brother Pierce and their friend Manny. However, they had little knowledge of the technology they used, and Pierce was, at some point before their first appearance, sucked into a Null Void Projector they had confused with a disintegrator weapon. Believing that Pierce was dead, Helen and Manny continued the work, capturing many kinds of aliens they confused for criminals and sending them into the Null Void. Though part of those they captured were DNAlien, most of them were probably Plumbers kids, according to Ben.

Alien Force
After capturing a DNAlien in Plumbers' Helpers, their alien scanner points out Ben, Gwen and Kevin Levin. Manny believes them to be aliens so he sets fire to a truck in hopes to see whether or not they are aliens. They then capture Kevin in hopes of leading Ben and Gwen to them. After a fight, Helen realizes they are not the enemy and that they have been sending the wrong aliens into the Null Void. Both Helen and Manny decide to go there in order to free those they had mistakenly trapped.

Helen reappears alongside Pierce and Manny in Voided working with Max Tennyson trying to stop D‘Void, who turns out to be Dr. Animo. She contacted Gwen to find help. Then along with the help of Ben and Max they defeat him.

In War of the Worlds: Part 2, Helen, alongside Pierce, Manny and Max help Ben defeat the Highbreed threat, once the threat is over she becomes a pupil of Max.

Helen makes another appearance in Above and Beyond (she gets attacked by Echo Echo) where Ben is supposedly attacking Max, But then it turns out to be a test and they are then told that because of their defeating Ben (as well as their heroic actions in trying to prevent the space station from hitting London) they are approved for training at the Plumbers' Academy.

Ultimate Alien
Helen was mentioned in Absolute Power: Part 1 by Alan, where he explained that her powers were stolen and killed by Ultimate Kevin like he did to Manny, Pierce, Dr. Viktor and Alan himself, although Alan didn't get killed. She was revived and got her powers back after Kevin was changed back to normal.

Helen appeared in a flashback in The Ultimate Enemy: Part 2.

Ben 10: Alien Force

 * Plumbers' Helpers (first appearance)
 * Voided
 * War of the Worlds: Part 2
 * Vengeance of Vilgax: Part 1
 * Above and Beyond

Ben 10: Ultimate Alien

 * The Ultimate Enemy: Part 2 (flashback; cameo)

Trivia

 * According to Dwayne McDuffie, Helen is Pierce's adopted sister though it is unknown how they met or what happened to their parents.
 * Helen was shown to have some sort of rivalry with Gwen as Manny had with Kevin.
 * Helen's name is wordplay on the phrase "hell on wheels", which is used to describe a person who likes to drive fast and/or recklessly.
 * In War of the Worlds: Part 2, it is shown that Helen has goggles similar as XLR8, having a mask while she was taking the guns in the hands of DNAliens.