Gwendolyn "Gwen" Tennyson is a main character from the Ben 10 series. She's the cousin to Ben Tennyson and granddaughter of Max Tennyson. Ever since her adventures with her family across the States in the first series, she has developed a skill at wielding magic by taking a spellbook from her arch-enemy, Charmcaster. As a counterpart to Ben's ability to use the Omnitrix, she's a helpful addition to Ben's team. At first, Ben and Gwen had a love/hate relationship with each other, showing concern for each other only when it felt necessary. In Ben 10: Alien Force, the two have abandoned their childhood quarrel and have become close. Since the addition of former enemy Kevin to the team, Gwen has easily spotted his crush on her and often exploits it. It is revealed in the Alien Force series that she is a descendent of an alien race of pure energy beings called Anodites; nevertheless, she chooses to remain with Ben and Kevin.
In FusionFall, Gwen can be found at the Pimpleback Mountains. When spoken to, she sometimes mentions getting constant e-mails from someone in Nowhere who knows about alien activity (it can easily be guessed that this is either Courage or Kevin). Her missions mainly involve the Totem plotline in which she sends the player to activate the totems spread across Downtown and the Wilds, which supposedly act as a self-defense mechanism.
Gwen can also be found inside of Ship, giving out the mission "Gwen's Gambit" and a Gwen 10,000 hood and shirt. She is mainly responsible for creating the portals that the player uses to infiltrate Vilgax's ship and providing the platforms that must be used to navigate the said ship.
- When the game was first released, Gwen's model had her original appearance in Alien Force. Once Season 3 of the series began airing, her model and those of Kevin and Vilgax were at that time changed to their current appearances. She and Kevin have so far not been updated with their Ben 10: Ultimate Alien appearances or Ben 10: Omniverse appearances.
- While Gwen was majorly involved in the Totem plotline, Fusion Gwen was also involved with the arc.