When a giant monster from the underwater land of Mu emerges, he threatens a full-scale invasion. He soon finds to his horror that an even larger creature has arrived, Ulvar. Ulvar causes Gigantus to think HIS race is on its way, and thus Gigantus returns to his home and warns his people not to return to the surface world. Ulvar, unbeknownst to him, was merely a large prop created by a human being to drive the creature away.

Gigantus was used by Kro, the Deviant, to attack the Monster Hunters when they arrived on Monster Island.

Gigantus was one of a number of creatures taken control of by a group of Skrulls hoping to flush out a traitor. They used the monsters to attack various Earth cities. It later returned as reinforcements for the Mole Man during a battle that included the Fantastic Four, Spider-Man and others.

Gigantus was among the monsters summoned by the Mole Man to greet Adam Warlock upon his arrival on Monster Island.

When the demon called Nightmare invaded the dreams of a young Peter Parker (the future Spider-Man), he used several monsters to attack Parker, including Gigantus.