Mark Grayson thought he had basically a perfect life. Since he was a kid, he knew his father was secretly Omni-Man, perhaps the most powerful superhero on Earth. His father was also part of an alien race known as the Vitrumites, a race that Mark's father claimed traveled throughout the universe on a mission of kindness and enlightenment.
When Mark was 17, his life got even better when he discovered that due to his half-Vitrumite heritage, he had powers similar to his father! Soon he began wearing a costume and acting as a superhero known as Invincible.
Seven issues into the "Invincible" series by writer Robert Kirkman and artist Cory Walker, the pre-eminent superhero team of the world, the Guardians of the Globe, were viciously murdered. The dramatic twist at the end of the issue (Walker's last issue as artist - Ryan Ottley took over the art chores with issue #8) was that the murderer was none other than Omni-Man!
In "Invincible" #11, Mark discovers that his father is a murderer and also learns that the Vitrumites are actually an evil race of predators. In fact, Omni-Man was sent to Earth in order to prepare the planet for a hostile takeover. We flash back to the happy origin Omni-Man had given Mark in Invincible #2 and learn the truth behind all of his father's seemingly heroic actions over the years. After explaining himself, Omni-Man looks to his son and tell him that as a half-Vitrumite, Mark is expected to join his father in the domination of Earth. As the truth dawns upon Mark, he realizes that his father truly views the people of Earth (including Mark's mother) as mere animals to be herded and ruled over.
Mark refuses his father's offer of partnership, and what follows in "Invincible" #12 is one of the bloodier superhero fights in the history of the medium.
In reality, Invincible cannot compete with his father's powers, as it is essentially an adult beating up a child, but Mark refuses to either give up or to join his father. He just keeps at it, as their battle travels the globe, with Omni-Man killing thousands throughout the course of the fight.
Ultimately, Mark is left battered and near death by his father who, at the last moment, for some unspoken reason – perhaps due to some spark of a familial bond – decides to spare his son and flies off into outer space, leaving behind a bloodied Invincible.