"Yipes! Couldn't you just give us a written quiz for a change, Professor? He looks as mean as the Sentinels and Lucifer's Ultra Androids rolled into one!" -- Iceman (Bobby Drake).
Professor X designed Colosso to serve as a challenge for the X-Men in the Danger Room, and instructed them to defeat Colosso in just five minutes. Angel flew at Colosso, but was struck down by its paralyzing ray. Iceman attempted to slip the robot with ice on the floor, but jets built into its legs melted the ice. Cyclops then fired an optic blast at it, but its body reflected the ray back, and nearly struck the Beast. The Beast attempted to strike it from behind, but its lights warned it of the attack, and it evaded him. It then captured Marvel Girl and Cyclops in its hands, but Cyclops had guessed the source of the robot's sensory powers, and Marvel Girl levitated Professor X's blanket around Colosso's head, rendering it blind. The Beast then tied the blanket into a knot, and the five X-Men attacked it together, and managed to topple Colosso over. Professor X was pleased that they had passed his test.
Dr. Doom gained access to the X-Mansion and reprogrammed Colosso to serve him, along with two Sentinels which were in the X-Men's possession. Colosso attacked Marvel Girl and Professor X, but they destroyed it.
To train the new team of X-Men, Cyclops used Colosso in the Danger Room, and had it battled Colossus, Wolverine and Thunderbird.
When the X-Mansion was controlled by Warhawk, he managed to capture the X-Men in the Danger Room, and unleashed Colosso upon Colossus. Colosso managed to capture Colossus with a spray of sticky paste. Wolverine was able to shut down the Danger Room, deactivating Colosso.
During a Danger Room session monitored by Banshee, Colosso again battled Colossus, and managed to outfight Colossus. Colossus finally managed to lift Colosso into the air and hurl him at Wolverine, who slashed Colosso into pieces with his claws.