Giganto was one of many Deviant Mutates dwelling on Monster Isle. The Mole Man made him his servant and used him to attack atomic power plants all over the world, including one in French equatorial Africa. When the Fantastic Four went to investigate, the Mole Man unleashed Giganto on the heroes but was held back by the Human Torch, allowing them to escape.
When the Skrulls landed on Monster Isle, like most other monsters, Giganto was subdued by their slave darts and teleported elsewhere on the Earth, in order to increase the mental stress level across the planet. When it was revealed that the reason for the Skrull's visit to earth was to retrieve the egg of an Inorganic Technotroid, an unstoppable robot created to imprint on the Skrull empress and act as her bodyguard. Instead, the egg was retrieved by Giganto. When it hatched, the Technotroid imprinted on Giganto and her mate instead and they adopted the robot as their own child.
