Cassie:

Cassie is the "Tree-hugger", as Marco calls her. She loves animals and helps her father run the Wildlife Rehabilitation Center, which is a clinic for injured animals. Her mother works at The Gardens, which is sort of like a zoo. Her favorite morphs are the wolf and the horse. She likes Jake.

Rachel:

Rachel is Cassie's best friend. Marco calls her Xena: Warrior Princess, because she is always gung ho about missions. She lives with her mother and her two sisters, Jordan and Sara. Jake is her cousin. She is often called a super model. Her favorite morph is the elephant.

Jake:

Jake is the leader. He has the capabilities to make life and death desisions, even when they involve his friends. He lives with his mother and father. Marco calls him their "fearless leader", although Jake says that he doesn't like being the leader. His brother Tom is a Controller.

Marco:

Marco is the joker. For some reason, he can make jokes when he is scared to death and there is a chance that they all might get killed. He likes to come up with names for every Animorph. He lives with his father. Only he and Jake know that his mother, who supposedly drowned, became a Contoller, infested by the Yeerk that is Visser 1.

Tobias:

Tobias is a red-tailed hawk. He was stuck in hawk form in the first book, down in a Yeerk pool. He lives in the woods, with Ax. His mother is Loren, and his father is Elfangor, the Andalite who gave the Animorphs thier powers.

Aximili-Esgarroth-Isthill:

Ax is Elfangor's younger brother. He was trapped on Earth after the Dome ship was shot down. He was the only survivor. He is an Andalite. He deeply despises Visser 3, who killed Elfangor.