Numero Uno's assistant (his name is unknown) is an inmate that seems to follow Numero Uno everywhere within the limits of St. Canard Minimum Security Prison. He serves as the rhino's caddie for his Golf play, sunbathes alongside him, and helps him with the barbacue.
He doesn't talk at all in his only appearence so he doesn't had a voice actor.
Numero Uno's assistant is obviously just a follower, not a leader, but it's never clear whatever he serves the wealthy rhino for an interest or because they are genuinely friends. Uno, in the other hand, probably saw him as a pal of sorts, since he invited his assistant to activities that don't really requiere assistance. It's also unknown if they were partners in crime before Uno ended in jail of if the assistant is convicted by unrelated crimes and meet Uno later in prison.
The assistant looks like he is really lazy, even apathetic, or at least that's what his character design implies, with his tired look, poor posture, and the way that his cap hides his eyes.
The assistant's species isn't very defined, he seems like a short kangaroo, or maybe an armadillo, he is probably the later, since his tail isn't visible.
He follows Uno as a Caddie when the rhino plays golf, then sunbathes with him, and later on, he is besides his boss when making barbacue.