Invincible (Mark Grayson): The main protagonist and son of Omni-Man. He discovers he has Viltrumite powers like flight and super-strength, and he works hard to protect Earth while dealing with the trauma of his heritage.

Shrinking Rae / Ray: A superhero who can shrink to microscopic proportions while retaining her physical stability and strength. In the comic, Ray is male, while in the animated series, Rae is female.

Rexsplode (Rex Sloan): A cocky former member of the Teen Team and Guardians of the Globe who can accelerate the molecular energy of objects to make them explode, often using his own body parts or coins as weapons.

Atom Eve (Samantha Eve Wilkins): A powerful superhero who can manipulate matter and energy at an atomic level, allowing her to construct shields, manipulate objects, and fly. She is Mark's close ally.

Cecil Stedman: The head of the Global Defense Agency (GDA). A pragmatic and ruthless government director who uses questionable methods and morally gray decisions to protect Earth from global and cosmic threats.

Omni-Man (Nolan Grayson): Mark's father and Earth's premier alien protector from the planet Viltrum. He initially pretends to be a noble protector before revealing his true mission to conquer Earth for the Viltrum Empire.

Robot (Rudy Conners): Initially appearing via robotic drone bodies, Rudy is a brilliant tactician and former leader of the Teen Team. Born with a severe birth defect that forced him to live in a life-support tank, he later transfers his consciousness into a cloned, healthy human body.

Monster Girl (Amanda): A hero cursed by a gypsy to transform into a massive, super-strong ogre-like creature. Each transformation physically ages her body backward into a child, creating severe personal and biological struggles.

A weak, attention-seeking superhero who constantly tries to impress Mark Grayson and the other heroes. Her power is Light Spark, letting her create tiny bursts of bright energy from her hands. They can briefly blind someone or make small explosions, but they're weak and quickly exhaust her. She often pretends her powers are stronger than they are, acts helpless so the stronger heroes will save her, and says things like, “I’m not like other heroes—I don’t need some super-powerful guy protecting me.” She gets jealous whenever another girl receives attention and constantly tries to prove she’s useful despite being one of the weaker heroes.