Gemini Man is one of the robot masters in Mega Man 3. He was co-created by Dr. Light and Dr. Wily, but Wily modified him into a battle robot to take down Mega Man.
His fight is pretty interesting. His Gemini Laser is pretty powerful, and he is one of the few bosses in the series than can split himself a clone.
After he's defeated you get his power. The gemini laser can bounce off walls until it hits a target or runs out of power.