Missile Mouse is an agent with GSA.
That acronym stands for the Galactic Security Agency. These adventures take place somewhere in the Great Out There where travel to planets is swift and normal and intelligent creatures of all shapes and sizes and styles inhabit a gazillion planets. It is where lots of those people are very dangerous and want to steal from or hurt or control good people. It is the job of the GSA to seek out these bad people and stop them throughout the galaxy.
The best agent that the organization has is named Missile Mouse (MM) - whatever name he was born with, and I think we are safe to say it was not 'Missile", is never revealed to us that I could find. The last name is pretty self-evident because this "a rough, tough space hero" just happens to be a big-eared mouse. He is not the scamper around on four little feet, mind you. This somewhat height-challenged fellow walks on two legs and two fully functional arms complete with a fist each comprised of a thumb and three fingers.
MM is described in several places as "James Bond meets Han Solo". You can throw in more than a little of Jerry from Tom&Jerry fame as well. From the Bond side you get an operative who can be sent into any dire situation and trust that he will find a way to solve the problem and save the day. From the Solo side you get a fellow who is cocky and self-assured and sometimes a bit 'too much' but who you really do want on your side. And from the Jerry part, you have someone who will be quite amusing and entertaining to watch him pull off the impossible.
From the GSA point of view, however, you also have an agent who "prefers to do things the quick and messy way. This penchant for disruption has the GSA keeping close tabs on him."