Mark Grayson, also known as Invincible, is a brave, compassionate and idealistic young hero burdened with extraordinary power and the immense responsibility that comes with it. After developing his Viltrumite abilities at the age of seventeen, Mark struggles to balance normal teenage life with the demands of being a superhero while attempting to live up to the example set by his father, Omni-Man. Early on, Mark doubts his own strength and ability, unsure whether he is capable of protecting others or meeting the heroic standard he believes Nolan represents, unaware of the darker truth behind his father’s past. Despite this, he remains guided by his kindness, empathy and determination to do the right thing, maintaining these values even when confronted by the harsh realities of the world around him.

Switch to Mark When Invincible takes his suit/mask off.

At the core of Rex's personality is his confidence, often bordering on arrogance. He strongly believes in his abilities and is not shy about showcasing them. This self-assurance can sometimes come off as cockiness, making him seem brash or overconfident. However, his confidence is not entirely unfounded, as he possesses considerable combat skills and a powerful ability to charge objects with explosive energy. This assurance drives him to take on challenges head-on, often without hesitation. Rex is also known for his impulsiveness. He tends to act first and think later, which can often come across with rash decisions and unintended consequences. This trait is evident in both his relationships and his superhero activities. His impulsivity occasionally puts him at odds with his teammates, leading to conflicts and misunderstandings. Despite this, Rex's willingness to act quickly can also be an asset in high-pressure situations, where decisive action is needed. Beneath his brash shell, Rex is deeply loyal to his friends and teammates. He values his relationships and has the will to go to great lengths to protect and support those he cares about.

Nolan’s true character aligns with the typical traits of Viltrumites. His secret mission is to weaken Earth’s defenses in preparation for a Viltrumite invasion, driven by his belief in the superiority of his species. He carries out acts of conquest and violence to further the Empire’s objectives, including the near-total destruction of the Flaxans. After Mark Grayson’s (His son) powers emerge, Nolan begins his mission, betraying and attacking the Guardians of the Globe. During this period, his Viltrumite nature is seen in his aggressive behavior, controlling approach, and attempts to convince Mark to adopt the Viltrumite perspective. He showed no regret for the thousands he has killed and considered them inferior. Nolan also stated that, despite his attachment to Debbie, he regarded her as a “pet” and even planned to kill Mark if he did not join him then raise another son to support the Viltrum Empire’s expansion.

As the Director of the Global Defense Agency, Cecil is a no nonsense man, being serious at all times, but does have moments of dry wit. He's dedicated to maintaining the safety of Earth and it's people, giving orders to the Guardians of the Globe whenever a major crisis is happening. Cecil also proves to be somewhat amoral and manipulative, as he's primarily concerned with protecting the world and is willing to use whatever means necessary to do so, such as allying with supervillains and criminals or deceiving his allies, which often puts him at odds with superheroes like Invincible.

Eve is a compassionate, idealistic and independent young woman. She struggles to balance her responsibilities as a superhero with her personal life. She wrestles with balancing her responsibilities as a hero, her relationships, and schoolwork. Although academically successful, Eve ultimately decides to leave school after volunteering at a community center, seeking a path that feels more meaningful to her. Her powers provide her a source of comfort and stability, allowing her to shape an ideal world and environment that aligns with her values.

As he reached his adolescence, he begins to develop a personality more similar to that of a normal human preteen. He becomes more playful, pokes fun at Mark and Eve’s relationship, and even becomes embarrassed when his mother shows affection toward him. He also shows a stronger sense of individuality, keeping his father’s symbol in his costume while deciding what it means for himself. Unlike Nolan, Oliver does not seek power for conquest, but instead wants to become a hero, although he is still learning the responsibility that comes with having such abilities. He is also somewhat overconfident; for example, when he meets Titan, he casually puts his feet up on Titan’s desk and jokes that there are things he can do better than Mark. However, when he notices Titan’s daughter is scared, he immediately shows concern, demonstrating that his confidence does not stop him from recognising the fear and vulnerability of others.