The story behind Rush X™ is a complicated, sad, and heartfelt one. Dr. Light decided to make X, his newest AI robot to act as a partner for Mega Man. As a suport unit for X, he built Rush X™.
Things were going fine, until one day, Zero came and killed Mega Man and Rush. Dr. Light came back from shopping, and noticed all his robots laying dead on the floor. He asked X who did it, and he framed Rush X™ for it. Dr Light didn't believe this though, and stuck X in a capsule for 30 years.
Rush X™ was mad that X tried to frame him, and turned the capsule up for even more years. Rush X™ then ran away, into hiding.
Years later, word that X was found came out, and Rush X™ decided to get his revenge on him by working with Sigma. He took on the name Velgauder, and failed at beating X. He went into hiding again until the MMZ series. He now hides in the shadows, waiting to ambush Zero, to take him to X.
"Rush X™ is a dog"