Mouse is the code name used by Morris L. Sanderson. He is one of six Screaming Eagles under the command of Sgt. Savage. Another character code named Mouse was in the Retaliation film. It is unclear if these are meant to be the same character or not.
Not much is known of Sanderson's life before Sgt. Savage took command of him and five other highly-trained, undisciplined soldiers. Sanderson and the other Screaming Eagles have since helped stop NASA from unwittingly deploying a cyber doomsday device, protect a nuclear facility, and served in maneuvers in the arctic before moving to reserve status.
Sanderson is the team's hacker. Soon after Savage took charge, Sanderson was able to get inside the head of an I.R.O.N. Army stormtrooper to get details on the International Orbital Space Platform. That information linked the platform to the I.R.O.N. Army and gave Savage he justification needed to stop the launch.
A Real American Hero continuity
Hasbro Comics continuity
Sanderson, along with the other Screaming Eagles, appear in the Sgt. Savage vs. Gen. Blitz mini-comics packed with select toys. In the comic, the Eagles defend a nuclear facility from the I.R.O.N. Army, drawing the enemy into a trap by hiding under the dirt of their bunker before attacking and driving back General Blitz's forces.
Devil's Due Comics continuity
During the conflict now known as World War III, Sanderson was stationed in Uganda in the equatorial Eastern Africa.
Sanderson's only known appearance in cartoon form is the single Sgt. Savage and his Screaming Eagles episode, Old Soldiers Never Die. Along with the other Eagles, Sanderson helps stop NASA from unwittingly deploying a cyber doomsday device.
There were no toys of Mouse released as part of the Sgt. Savage and his Screaming Eagles toyline. A figure was released in 2013 in support of the Retaliation film, but no file card was included, so it is unclear if the two characters are meant to be the same.
Mouse at My Useless Knowledge