The XCOR Prototype X-Racer is a competition air racing racer rocketplane. It is a heavily modified Velocity SE, and a development of the EZ-Rocket by XCOR. It was contracted for by the Rocket Racing League of Peter Diamandis (founder of the X-Prize Foundation). This plane served as the prototype for the Rocket Racing League Rocket Racer. The RRL concept was to drive development of rocket engine technologies, and this also served for development of XCOR's rocket engine technology. A further development of the engine technology was used in the XCOR Lynx.