- Winnie Foster: A 10-year-old girl who lives in the village of Treegap. She is curious and adventurous, and she befriends the immortal Tucks.
- Jesse Tuck: The youngest of the Tuck brothers. He is kind and gentle, and he falls in love with Winnie.
- Mae Tuck: Jesse's mother. She is a strong and protective woman, and she is willing to do whatever it takes to keep her family safe.
- Angus Tuck: Jesse's father. He is a wise and gentle man, and he is the one who discovered the spring of eternal life.
- Miles Tuck: Jesse's older brother. He is more reckless and impulsive than Jesse, and he is often the one who gets the Tucks into trouble.
Other characters:
- The Man in the Yellow Suit: A mysterious stranger who comes to Treegap and tries to capture the Tucks.
- The Constable: The law enforcement officer in Treegap. He is suspicious of the Tucks and tries to arrest them.
- The Doctor: A doctor who comes to Treegap to help Winnie after she is injured. He is fascinated by the Tucks and their secret of eternal life.
- The Narrator: The story is told by an unnamed narrator who is a friend of Winnie's family.