Mouse is the code name used by Morris L. Sanderson. Not much is known of his life before Sgt. Savage took command of Sanderson and five other highly-trained, undisciplined sergeants, to form the Screaming Eagles. Sanderson is the team's hacker.
A Real American Hero continuity
Hasbro Comics continuity
Sanderson, along with the other Screaming Eagles, defends 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.
While on maneuvers in the Arctic, the Screaming Eagles were ambushed by a platoon of Arctic Stormtroopers. Despite heavy artillery bombardment the team managed to escape, racking up a few scrapped Stormtroopers on the way. 
Devil's Due Comics continuity
During the conflict now known as World War III, Sanderson was stationed in Uganda in the equatorial region of eastern Africa.
Soon after Savage took charge, Sanderson was able to access the memory 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 the justification needed to stop the launch, preventing 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.
Mouse at My Useless Knowledge