Boxer Barry is a shirtless, muscular black man wearing boxer pants and red boxer gloves on his hands, as well as blue boots (orange in SS1). However, he is unable to use his gloves in melee combat and they don't even show up in the first person view models.
Based on his character select screen quote, he has never won a match. This might explain why he's taken to killing Mental's forces instead of continuing to do boxing.
In Serious Sam HD, he has a new and completely different model, but still looks similar to his original version.