Gwen Tennyson

Gwendolyn Tennyson, known simply as Gwen, is Ben's cousin and a secondary protagonist in each series. Gwen was first introduced in And Then There Were 10, when her parents send her on a summer-long trip with her Grandpa Max and her cousin Ben. Like Ben, she is a Human/Anodite hybrid, but unlike her father, uncle, brother or cousin, she has, as her Grandmother refers to it, "the spark."

Ben 10 Alien Force
In the sequel series, Ben 10: Alien Force, fifteen-year-old Gwen has grown into a calm, confident, and collective teenager, and she and Ben get along much better and are no longer openly hostile towards one another (most of the time). In this series during seasons 1-2, Gwen wears a plain, white shirt, loosely buttoned blue sweater, a black skirt with black tights, her hair is much longer and darker and her eyes are much darker as well. Gwen is now a black belt (taking classes in Tae Kwon Do, according to dialogue in Simple), but tends to favor using her powers. She is able to create energy constructs for nearly any purpose, usually creating platforms to levitate herself (and others), beams to grab enemies, circular blasts to knock enemies back, projecting beams from her eyes that seem to simulate heat vision, and opening up interdimensional portals. In Ben 10,000, her future self is able to create time portals. She also has a wide range of other loosely defined supernatural abilities, such as dowsing, limited telepathy, and clairvoyance. In the episode Everybody Talks About the Weather, Kevin says she gets her powers from her alien bloodline, but she refuses to believe him. Little does she know that she would realize he was right in What Are Little Girls Made Of? Her powers are revealed to be alien in origin; her grandmother, Verdona, is an energy being known as an Anodite and surprisingly she is the only descendant of hers who inherited Verdona's powers. Verdona tells Gwen that what she and others originally thought of as "magic" was actually the manipulation of mana, a substance of magic - making Anodites a magic-wielding race. Verdona offers to take Gwen to her home planet and train her in the mystical ways of the Anodites, but Gwen prefers to remain on Earth with Ben and Kevin. She hates being called an "energy being", referring to her Anodite heritage. In the episode, In Charm's Way, it's implied that highly gifted humans like Charmcaster can also be trained to utilize mana.

In episode eleven of the second season, Unearthed, an alien creature is able to see her as an Anodite, in which she looks exactly like her grandmother's true form, but slightly shorter. In the two-part season two finale War of the Worlds when Kevin was threatened by a Highbreed commander, she assumes her dormant Anodite form for the first time and easily defeats the commander with an exceedingly strong powerful burst of pure pink glowing energy. She was almost overwhelmed by her own power before Kevin snaps her out of it. Gwen in Season 3 of Alien Force, during the course of the series she has developed a romantic relationship with Kevin. They have also been shown to have arguments, usually starting with Gwen always trying to force Kevin to "Ask her out." and him always answering "Don't push me." In the episode Fool's Gold, Kevin appears to be avoiding her because he is ashamed of his recent mutation due to accidentally absorbing a massive feedback pulse as a result of trying to hack the Omnitrix. She was unaffected by the blast because she put an energy shield around herself. Kevin gives her a locket of the two of them when he was in his human form, asking her to remember him as he was. Gwen says she doesn't care what he looks like, and he replies "But I do". In the two part season three premiere, Vengeance of Vilgax, Ben and Gwen seem to have revived their infamous rivalry from the original series, in part due to Ben's cockiness and inflated ego. In the same episode, Gwen pours a smoothie over Ben's head, and he nearly returns the favor. Despite their rivalry, they both still have a strong bond, visible in the episode In Charm's Way, when Ben defends Gwen and informs Kevin that she has been spending all of her spare time in order to find a cure for Kevin's condition. It is shown in both Vengeance of Vilgax: Part 2 and Inferno, respectively, that Gwen suffers from both. arachnophobia and claustrophobia.

Unlike the original series, Gwen has worn other costumes besides her usual clothing. In the episode Time Heals, it was revealed that Gwen kept her Lucky Girl costume. In What Are Little Girls Made Of? Gwen is shown to have a white bikini. In Charm's Way, she has a black bikini. In The Con of Rath, she is shown wearing another one piece black bikini, pink flip flops, a hat, sunglasses, and a pink towel skirt. She also has a karate suit. In Save the Last Dance, Gwen was seen wearing a formal outfit (a white strapless prom dress).She has kept and worn her Lucky Girl costume, which is now bigger with Gwen being fifteen.

Jimmy 10
She was only mentioned in Jimmy 10 by Kevin.

Tennyson Force
She is one of the main villians in Tennyson Force along with Kevin. She is really smart now and has curly hair instead of strait.