Omni-Man is believed to have always been evil, as he was sent to Earth to conquer it in order to create a home for the surviving Viltrumite race.
Omni-Man, whose Earth name is Nolan Grayson, is a deuteragonist and the main villain of the Invincible comic book series. Omni-Man was also the main antagonist of season one of the animated adaptation of the comic, which debuted in 2021. He is Oliver Grayson’s father, who is known by his superheo name, Invincible. Omni-Man is part of the Viltrumite race. His superpowers range from super strength, speed, immortality and the ability to fly.
In order to understand why Omni-Man turned evil, it is important to understand the reason for him coming to Earth in the first place. He came to Earth to conquer the planet. This is due to his planet suffering from a deadly plague, which threatened to end their existence as it ravaged through his species. However, in coming to Earth, Omni-Man first infiltrated the people he lived with by assuming his alias as Nolan Grayson.
Following infiltrating the community he integrated into, he found love and got married to a human. Moreover, he fell in love with humanity. Therefore, he did not necessarily turn evil as his initial intention of being on Earth was to conquer the planet. However, his guise was to pose as a superhero. Therefore, Omni-Man serves as an anti-hero, as he is continually in conflict with himself to follow his intended purpose, or choosing love as he does love humanity, his wife and the life he has created for himself.
This is further showcased by his decision to have children with a human, an action which was prohibited before the deadly plague which ravaged his race happened. However, when the Viltrumite race was once again facing extinction, the act was less frowned upon.