General Ursus is very much the stereotyped "mad general", on top of being a brutish gorilla. He sees little past the end of his own nose, and is interested mainly in his own dreams of conquest, glory and power. At a meeting of the ape council, Ursus uses the recent crop failures, drought, and raids by wild humans as the basis for a call to invade the Forbidden Zone, where no ape has trodden (with rare exception) since the beginning of their world. Suggesting that another tribe of humans lives there (a belief based on Dr. Zaius' encounter with Taylor in the previous film), and the disappearances of gorilla scouts (save one who returned delirious) sent into the zone to investigate, Ursus stirs the apes up to invade, and claim their food source ("If they live, then they must eat!") for themselves.
Successful in persuading the apes to declare "a holy war" against the unknown, General Ursus assembles a gorilla army, and marches toward the Forbidden Zone, accompanied by Minister of Science Dr. Zaius — who has his misgivings about the whole adventure, but goes along for the sake of science, and "the faith" of the apes.
Indeed, a small group of intelligent mutant humans do dwell in the Forbidden Zone, underground among the ruins of New York City. While their physical features have been mutated by generations living in the irradiated area, they have advanced psychic powers, which are their only line of defense against "enemies", i.e. any outsiders. Learning that the gorilla army is on its way, the mutants plant terrifying visions in their minds, of crucified and tortured apes surrounded by fire, and finally the familiar statue of the Lawgiver, prophet of the apes, beginning to crack and bleed. Ursus is frightened as are his soldiers. Having gone too far with their exposition, the mutants' vision backfires by instilling rage in Dr. Zaius, and he rides into the heart of the vision, remaining unharmed. It grates Ursus that Zaius has shown him up, but he orders the army to advance, and they soon find the entrance to the mutant city.
With their mental powers useless against the "thick-skulled" apes, the mutants have only one other weapon available — their "god" or idol, a 20th century nuclear missile with a cobalt casing capable of igniting the atmosphere and extinguishing all life on Earth. While the weapon has been passed down through generations, and forms the basis of the mutant culture, left unsaid (but implied by the mutants calling it the "Divine Bomb") is whether the mutants know of its true destructive power.
Leading the gorilla army into the heart of the mutant world (the former cathedral which now houses the Divine Bomb), Ursus and the other apes are taken back momentarily when first a mutant (their leader Méndez) speaks, declaring "This is the instrument of my god!" then the bomb rises into launch position. Recovering quickly, Ursus orders his sergeant to take Méndez into custody, but the sergeant shoots Méndez instead. Ursus taunts "Your god didn't save you, did he?!" as he falls. Thinking the missile is little more than a worshiped idol, Ursus orders a block and tackle be set up, to pull it down.
Zaius pleads with General Ursus not to touch the missile, knowing only "That weapon was built by Man!" and "It'll kill us all!", but Ursus ignores him, even when the missile shell cracks open and toxic gas escapes, waylaying the nearby gorillas. Ursus is finally killed by a rifle shot, as humans Taylor and Brent vainly try to stop the gorilla army, only moments before the bomb is detonated, putting an end to the gorilla's ambitions — along with everything else on the planet.