"Invincible" is built on a series of devastating plot twists that redefine the narrative. The first and most critical twist is the revelation at the end of Episode 1 that Omni-Man, Mark's father and the world's greatest hero, is a cold-blooded murderer who slaughters the Guardians of the Globe. This act is not due to mind control but is a calculated first step in his true mission: to weaken Earth for a takeover by the Viltrumite Empire.
The Season 1 finale reveals the full truth: the Viltrumites are not benevolent protectors but a race of brutal conquerors who achieved a 'utopia' by culling their weak and now expand their empire across the galaxy. Nolan's entire life on Earth, including his marriage to Debbie, was part of his long-term mission. He calls his wife a "pet" in a moment of cruelty. However, his love for Mark proves to be his undoing. When he cannot bring himself to kill his son, he tearfully flees the planet, abandoning his mission and becoming a traitor to the Empire.
In Season 2, it is revealed that Nolan has taken refuge on the planet Thraxa and has fathered another child. He is tracked down by the Viltrumites, beaten, and taken prisoner to await execution. Before being captured, he tells Mark to read his books, implying they contain secrets to defeating the Viltrumites. The season's other major arc involves Angstrom Levy, a man who gains the memories of his infinite multiverse counterparts, many of whom were killed by evil versions of Invincible. This drives him to seek revenge, culminating in him holding Mark's family hostage. Mark, in a fit of uncontrollable rage, beats Levy to a bloody pulp, killing him. This act of killing, his first, deeply traumatizes Mark, as it confirms his greatest fear: that he has the same capacity for brutal violence as his father.