Battle Beast is a brutish Leonine warrior who seeks worthy opponents to fight across the universe. While savage and sadistic upon defeating his enemies, Battle Beast still shows an honor in his refusal to kill weak, unworthy foes. Previously, he viewed his empowering thirst for battle as a gift but soon realised it was a curse. Battle Beast believes the only way he can free himself of this curse is through the glorious death he so greatly desires.

He is a version of Mark Grayson that comes from a different multiverse. In his universe, he still becomes Invincible, only he chose the path of a supervillain. Stripevincible aided his evil alien father, Omni-Man, in conquering Earth. Now, Invincible is an ally of the Viltrum Empire, as shown in his different suit. This variant is a lot louder and prouder than the others, likely a result of being around the mighty Viltrumites.

Allen the Alien, or simply Allen, is a Unopan and a representative of the Coalition of Planets. He was born in breeding camps designed as a way to repopulate the Unopans after they were nearly wiped out by the Viltrumites, as well as a sort of countermeasure against them. While his role as a Viltrumite countermeasure did not succeed, he would go on to become an evaluation officer for the Coalition, visiting different planets across various galaxies in hopes of finding a warrior strong enough to stand against the Viltrumites. After a close brush with death, Allen gained increased strength and was able to compete with the elite Viltrumites in combat.

Cecil Stedman is a major character in Invincible. He is the director of the Global Defense Agency. Following the massacre of the Guardians of the Globe, he sought to identify the murderer but quickly realized it was actually Omni-Man. Since his departure from Earth, he began the creation of numerous advanced superhuman soldiers to get ready for the upcoming invasion.

Deborah "Debbie" Grayson is a major character in Invincible, serving as one of the deuteragonists of Season 1 and tritagonists of Season 2 and onward. She is the wife of Nolan Grayson, the mother of Mark and legal stepmother of Oliver Grayson. For two decades, Debbie and Nolan have shared a beautiful affectionate life alongside their son Mark, who would later become the superhero Invincible. Upon uncovering the reality of Nolan's afflictions, she begins to question everything she once understood, grappling with the truth that the man she thought she knew and loved was just a façade, all the while caring for her son Mark and her new stepson Oliver. She later starts a new relationship with her coworker, Paul, while coping with the recent trauma from her encounter with Angstrom Levy.

Jack, also known as Samurai Jack or simply the Samurai, is the alias taken by a Japanese warrior prince; with an unknown birth name; who acts as the titular protagonist of the cartoon, Samurai Jack. Since youth, Jack trained in many different areas under numerous teachers in a variety of skills and wielded his father's magical sword to defeat the demon Aku. However, Aku's time travel spell sent Jack eons into The Future, where he ruled all of Earth unopposed. Jack made it his mission to find a way back to his time and prevent Aku's dystopia. Throughout his travels, Jack became an infamous freedom fighter, protecting and aiding numerous civilizations and innocents terrorized by Aku's forces and other malevolent foes. Due to his many revolts against Aku's rule and being the only person capable of killing him because of his divinely crafted sword, he was the most wanted man in the world.

Markus Sebastian "Mark" Grayson is the main protagonist of the series of the same name. He is a Viltrumite-Human hybrid superhero Invincible, the son of Nolan and Debbie Grayson, the paternal older half-brother of Oliver Grayson, the boyfriend of Eve Wilkins/Atom Eve. Born as a Viltrumite-Human, Mark would ultimately gain his powers and start training to become a hero under his father's mentorship. Following a short involvement with the Teen Team, Mark teamed up with Atom Eve, the second version of the Guardians of the Globe, and Cecil Stedman from the G.D.A. to safeguard Earth from all known threats, while also attempting to protect Earth and the entire galaxy from the dangers presented by the Viltrum Empire.

This variation of the Viltrumite hybrid, Mark Grayson, has gone down a far more brutal path than the original one. On his Earth, no one can stand against him as he's completely toppled all the ruling powers and established himself as the dominat force globally. His Viltrumite DNA allowed him to wipe out the heroes of his world with minimal effort and now fear is the thing that keeps the planet spinning. One of the only people he ever genuinely cared about was his universe's William.