Asylum: Return of Sigma is a movie in the Asylum science fiction franchise.
- Alexandra McLean: An adventurous young human girl who always likes a good challenge.
- Koyi: a young twi'lek woman and one of Alexandra's best friends. She is a streetwise blue skin who was living on the street for twelve years after her parents were killed in a Fen Domar attack. Like Alexandra, she doesn't walk away from a challenge.
- Shoran: a muscular wookiee boy who is always getting into trouble. He sometimes tries to find a logical solution to some problems.
- Tom: a streetwise bad boy who tends to be a combination of cautious and cowardly. He sometimes says to his friends, "If I weren't such a coward where would you guys be".
- Zack: a sometimes fierce tempered young man whose parents were killed a Fen Domar attack. He has a scar on his hand where a Fen Domar struck him.
- Lucy Willings: a friend of Rex Chance, one of the last sigma combinations (combined with a Galapagos Tortoise) she has lived over 900 years because of her combinations and a formula that allowed her to live forever. She now works as a science teacher.
- Rex Chance: a man from 1937 who was placed in stasis. He was the first product of the Sigma experiment (a human combined with many animal traits). Today, he a greed to help stop a cyborg decendent of Upton Julius.
- Franklin Julius: a soldier and decendent of Upton Julius, he planned to use the Sigma Technology to defeat the Fen Domar and conquer the rest of the galaxy.