Gwendolyn "Gwen" Tennyson is Ben's ten-year old cousin (fifteen in Alien Force, and sixteen in Ultimate Alien [the two share the same birthday])..
In the original series, Gwen shares a love-hate relationship with Ben,
is a capable gymnast, and has had some training in martial arts.Overall, her most notable skill is her innate, if latent, power and ability at magic Gwen is capable of using various magical artifacts, charms, talismans, spell books and spells.