Gwendolyn Catherine "Gwen" Tennyson (voiced by Meagan Smith in the original series and Omniverse and Ashley Johnson in three sequels) is a character in Ben 10, Ben 10: Alien Force, Ben 10: Ultimate Alien, and Ben 10 Omniverse. She is the granddaughter of Grandpa Maxwell "Max Tennyson and the cousin of Benjamin Kirby "Ben" Tennyson.
- Ben 10 - Gwen Tennyson is depicted as a kind and intelligent girl, but she is a bit sarcastic and Ben and Gwen often argue and she is usually the one that makes the argument worse. Overall her most powerful skill is her innate, if latent, ability at magic.
- Ben 10: Alien Force - Gwen Tennyson reunites with Ben at the beginning of episode.
- Ben 10: Ultimate Alien - Gwen, Kevin and Ben team up with Max Tennyson to take down Aggregor.
- Ben 10 Omniverse - Gwen is no longer Ben's partner after she went to college.
- Ben 10 - Gwen Tennyson has orange hair and green eyes, she wears a blue and baby blue colored shirt, whit shorts, and black and white tennis shoes.
- Ben 10: Alien Force - Gwen Tennyson wore a white shirt under a dark blue sweater, black stockings under a black mini skirt, and black high heels. Her hair has also grown longer and is now down to her waist. In the third season, she wears a red shirt paired with a black vest, gray pants, and black flats. Her hair is worn in a high ponytail. In her Anodite form, she looks like a mini version of Verdona. At the beach, Gwen wore a black bikini. Later on, she wore a white one.
- Ben 10: Ultimate Alien - Gwen's outfit is similar to her outfit from the first two seasons of Alien Force, but with a red sweater while her hair still is now slicked back in a ponytail.
- Ben 10 Omniverse - Gwen Tennyson has orange hair and green eyes, she wears a blue-turquoise and white colored shirt with a dark grey dress, she wears socks pulled up to her knees and black shoes.