Rush (ラッシュ Rasshu?) is Mega Man's faithful robotic dog, created by Dr. Light to assist Mega Man in his travels.
Rush was named after the game Rush & Crash.
Rush's character concept appears to be loosely based on Friender, a support unit of Neo-Human Casshern, a Tatsunoko character, since Friender has the same ability of transforming into various vehicles for Casshern. Friender can be seen transforming into a jet, a drill-tank, and a submarine similar to Rush.
In the Ruby Spears cartoon, Rush is modeled after Scooby-Doo, as is evident from his goofy antics, garbled English and his love of "Battery Biscuits" (the cartoon's equivalent of "Scooby Snacks") to coerce him into performing the tasks given to or pleaded of him by the characters. The series' first episode showed Rush possessed a wide variety of transformation abilities not seen in the games, although he rarely transformed into anything besides his jet form throughout the series. He is shown capable of removing his helmet, although this was not shown in full capacity. Rush also had his own theme music, which was considerably goofier compared to the rest of the show's soundtrack.
Rush Bike may have been inspired by Rush Cycle and/or Rush Cannon, two entries submitted in a contest for fans to design a Robot Master.
In Mega Man: Upon A Star and the Ruby-Spears series, it is shown that Rush can speak and that he alternates between making typical dog sounds and speaking, but most of the time he only parrots other characters and also appears to have a limited ability for independent speech. This is possibly why in Rush's Mega Man & Bass CD data he has a quote, while Rush's counterpart Treble only says "Grrrrrrr". This may be due in some part to the fact that dogs can be taught limited speech while wolves, the basis of Treble's design, neither have patience nor capacity to do so.