Roller is a rollerback and Lee's pet.
Roller is rescued from a fighting arena alongside his friends. He immediately took a liking to Lee Powalski due to him being gentle towards him.
Roller can be moody and lazy but he is always ready for action.
He is able to roll himself into a ball and propel himself with his thrusters, allowing him to move around and turn quickly, and even jump into the air, spinning fast, and crashing into a threat. He can also spit adhesive agent onto enemies to slow them, allowing him to roll on them or hit them with his tail easier. If an enemy is behind Roller, he will strike with his tail or activate his thrusters to burn anyone behind. He can also use his gravity generator to manipulate his plating, launching it at other enemies and reattaching it after its launched or torn off.
Roller hates the sight of fire and will shy away from an enemy with fire abilities. However, he will ensure his master's safety.
Trivia:
Roller is named after his species.
He is the only machine that can roll.