Gwendolyn Catherine "Gwen" Tennyson is Ben Tennyson's ten-year old cousin. She shares a love-hate family relationship with Ben, and helps him by using her innate cleverness and intelligence. She is known to be a capable gymnast and martial artist and has received a black belt in taekwondo.
Overall, her most notable skill is her incredibly strong magical powers and abilities. Having within her what Charmcaster calls a magical aura, Gwen is capable of using various magical artifacts, charms, talismans, spellbooks and spells. She and Charmcaster are rivals, and they too share a love-hate relationship with each other and always enjoy their magical duels.