A gigantic dinosaur resembling a Tyrannosaurus Rex, Gorosaurus was first discovered on Mondo Island when he attacked Susan Watson, one of the UN submarine members who was sent to investigate the tiny isle. King Kong awoke and fought the ferocious reptile. It looked as though Gorosaurus was going to win, as he was able to knock King Kong over several times with his kangaroo kick. It was a devastating attack where the athletic animal would lean back on his tail and kick at his foe. Gorosaurus' luck would soon fail, however, when King Kong snapped his jaw. The injured dinosaur lay motionless on the ground, and seemed to be dead. He managed to hold on and recover, however, and soon sought a new home.

Gorosaurus lived peacefully on Monster Island for several years, until the island's inhabitants were eventually transported to Monster Land on Ogasawara Island. In 1999, the sinister alien race known as the Kilaakian took control of all the monsters, including Gorosaurus, and sent them to attack the Earth's major cities. Gorosaurus was ordered to ruthlessly attack and destroy Paris. Later, when the Kilaaks lost control of the monsters, they sent King Ghidorah to defeat them. Gorosaurus bravely charged King Ghidorah, but the space demon's gravity beams repelled him. As Anguirus and Godzilla assaulted King Ghidorah from the front, Gorosaurus was able to prepare an attack from behind. The determined dinosaur lashed out with his kangaroo kick. The powerful technique knocked the hateful hydra straight off his feet. Gorosaurus continued the onslaught by sinking his teeth into King Ghidorah’s tail, while Godzilla, Anguirus, and Minilla finished off the terrible tyrant. The awful space monster, which had destroyed so many lives, had himself finally met his demise. King Ghidorah's reign of terror was finally over, forever.

Gorosaurus was returned to Monster Land, where he continued to peacefully live out the rest of his life with his fellow monsters.