Double is a minor antagonist from Megaman X4. He serves as a reploid navigator who helps X and the other Maverick Hunters as an assistant but in reality he's a maverick working for Sigma as a double agent. He was given the order to infiltrate the Maverick Hunter ranks taking advantage of X's overly trusting nature to get closer to him and kill him if ordered to.

For a time while under his disguise as a navigator, Double's appearance is that of a pudgy and clumsy reploid in yellow armor which gives him an innocent facade. In his true form he's taller and more sleek with a build fit for combat. His armor is still mostly yellow but his limbs near the elbows and knees are a transparent pink, likely due to flowing energy or some goo substance. His shoulder pads, helmet along the back and the ends of his boots have a spike shaped protrusion to it and his eyes are purely red.

Contrary to his more innocent form, his combat form is more nimble. His body can generate wide energy waves and even miniature blobs that morph into small attack drones. In close combat he can even materialize a plasma energy blade from either arm.