Invincible is an animated TV series based on a comic book. It tells the story of Mark Grayson, son of Debbie, a realtor, and Nolan, who happens to be the most powerful superhero on Earth (Omni-Man). When Mark comes of age, his powers begin showing, and his father trains him for the superhero life. Mark takes the superhero name "Invincible".
Omni-Man has never joined the Guardians of the Globe, but he usually helps out in times of crises - he just doesn't want to answer to the Global Defense Agency, he claims. In the series' first episode, Omni-Man sends a false summons signal to the Guardians to meet in their headquarters and brutally kills them all, almost dying in the process. When GDA enter the scene, they assume Omni-Man is also a victim to the unknown danger out there. Meanwhile, Mark joins with the Teen Team, a group of young superheroes, to protect the world from invaders while all its major superheroes are dying or in a coma. One of the Teen Team is a schoolmate of Mark's, nicknamed Atom Eve. Teen Team and Invincible manage to hold off the invaders until a recuperated Omni-Man rejoins the battle. (The show makes a point of that Omni-Man's probably asking the invaders nicely to leave and not come back, but in reality, he's committing genocide). Meanwhile, a demon detective, Darkblood, investigates the Guardians' death and theorizes that the killer was one of the superheroes present.