Main •
Lucas Cruikshank as Marvin Forman, a "teenage" alien from the planet Klooton who is revealed to actually be 580 years old in "Pilot" and hides his true alien form behind his human form. His powers include the ability to freeze and heat objects at will using his fingers. He is also able to talk to animals, shapeshift, float, and calm people down using the "Klootonian Calm Palm". In the pilot, he adopts the name Marvin Marvin because he knew Teri did not want him to have the same last name as her. He nervously repeated his first name Marvin as his last name. • Mim Drew as Elizabeth "Liz" Forman, the family's mother and human "mother" of Marvin. She treats Marvin like her own children and really cares for him. •
Victory Van Tuyl as Teri Forman, the older sister of Henry and the younger human sister of Marvin. •
Jacob Bertrand as Henry Forman, Teri and Marvin's younger brother; he turns 10 in the episode "Burger on a Bun". He is very mischievous and cunning with plans of secret parties, playing hooky, going to a nude beach on a family vacation, etc. • Camille Spirlin as Brianna, Teri's very loyal best friend. She finds out about Marvin's secret in "Space-Cation". •
Pat Finn as Robert "Bob" Forman, the family's father and human "father" of Marvin. •
Casey Sander as George "Pop-Pop", Teri and Henry's grandfather, Marvin's human "grandfather," and the father of Liz. He is very childish and mischievous like his grandson Henry.
Recurring • Angel Amaral as Ben, Marvin's human best friend. He is stereotypically nerdy and is not very popular. He quickly makes friends with Marvin when he sees that Marvin is not making friends easily. Ben is also known to have a huge comic book collection. • Dennis Atlas as Derek Winfeld, a school kid who believes he is a horse. He grows his hair long and wears brown as he gallops through the school whinnying. ==Episodes==