Rush is a supporting character from the original Mega Man series of action platformer games. He is the robotic dog belonging to Mega Man in the games. He was introduced in Mega Man 3, and has appeared in nearly every game since.
Created by Dr. Light and Dr. Wily to be an all around support unit, Rush has the ability to transform into at least two different forms; Rush Marine and Rush Jet. As Rush Marine, Rush becomes a small, one-seated submarine while Rush Jet transforms his legs into jet engines that let him take flight. Rush also has the Rush Coil, which is a spring that pops out of his back and helps Mega Man reach higher platforms that he normally otherwise couldn't.
In later games, he can attach himself to Mega Man and make a Jet Adapter, which lets Mega Man perform a double jump, a Power Adapter, which lets Mega Man fire a very strong Mega Buster blast, and a Super Adapter, which is a somewhat fusion of the previous two, allowing Mega Man to double jump as well as launch his arm like a projectile (similar to the "Mega Arm" of Mega Man V).
Rush Cycle, where Rush transforms into a motorcyle for his master to ride, appeared in Mega Man 8.
Rush appears in the latest installment of the series, Mega Man 10.