Jack Shindo and Stanely Haggard are members of the first manned expedition to Mars, and on the red planet find a giant slug-like monster, Goudes/Gudis. Suddenly a giant warrior, Ultraman Great, arrives and fights Goudes, but is knocked down for a period. Shindo is pinned by a rockslide and Haggard tries to escape in their ship but is blown up by Gudis. It is then that Ultraman gets up, and when he is on the verge of victory Goudes changes into a virus and travels to Earth, where it mutates other creatures into monsters and awakens existing ones. Needing a human host to survive on Earth, Ultraman joins with Jack, allowing him to become the mighty alien when all seems lost. He joins UMA in order to help them battle the monsters. Halfway through the series a new Goudes, more powerful than the first, appears. It imprisons Ultraman, but Jack ultimately shows it the futility of its mission. Even if it does manage to corrupt all life, eventually there will be nothing else to corrupt, and Goudes is destroyed once and for all. For the rest of the series the environmental themes are stronger and the monsters usually arise from human pollution. In the series finale a doomsday scenario begins with the appearance of three powerful monsters; Kilazee, Kodalar, and the Earth itself, which tries to wipe out the human race for abusing it. Ultraman is defeated by Kodalar, but Jack survives. Ultimately the humans use an ancient disc to destroy Kodalar by reflecting its own power at it and Ultraman defeats Kilazee and carries it into space. The victory is seen as another chance for the human race.