In the 1991 film Godzilla vs. King Ghidorah, Godzilla's orgin in detail (at least for the "Heisei" series) was revealed! Godzilla was originally a dinosaur, named the "Godzillasaurus," who lived on Lagos Island. In 1994, during World War II, a Japanese garrison was attacked by Americans on Lagos. As the battle continued, Godzillasaurus appeared, and killed the American forces. An offshore battleship attacked the Godzillasaurus, and wounded him. Before the Japanese garrison left, they visited their wounded savior, and thanked him for saving their lives. In 1954, an H-Bomb test took place on a nearby island called Bikini. The radiation mutated the Godzillasaurus into the original Godzilla.

In 1992, people from the 23rd century came back to the 20th century and asked for help to transport the Godzillasaurus far from Lagos Island, so Godzilla will not exist in the future. The Futurians, as the people from the 23rd century became known as, traveled back to 1944, and teleported the Godzillasaurus to the Bering Sea, far away from the H-Bomb test that would take place in the future. Godzilla's creation though still could not be avoided. The Godzillasaurus, who was slowly turning into Godzilla, attacked a modern nuclear submarine, and grew to be 100m tall, twice as big as the original Godzilla. The Futurians plan to rid Godzilla had failed.