Hipp and Hopp were a pair of street gang members who had been on death row after inadvertantly shooting one of General Smiths' men. The General had agreed to call off their execution if they gave up their past human lives and join his mutated army.
Their original names didn't matter. To the outside world their human selves were oficially dead, their memories wiped.
Hipp was one of the earliest subjects. After reciving an accidental overdose, the only safe form for him to take was a very fat, 6 foot tall 500lb hippo. They incresaed his muscles to enable him to stay mobile and hold all that flab in place.
Hopp was a jackrabbit, with enhanced hearing, speed and leaping abilities. He didn't wear boots as they affected his running and leaping skills.
One day Hipp was relaxing in his heated mudhole when Hopp came running up. "We've got a special mission, Bro!" he said "We've to report for briefing ASAP!"