I can't speak much to the "general appearance" part without more details. What do you mean he doesn't keep it up? Doesn't tuck his shirt in or comes to work with large holes in his pants?
As for the odor part, you have to be careful with this. Does he have a MEDICAL condition that could be doing this? If an employee's body odor is caused by a medical condition and you don't deal with it correctly, there is the Americans with Disabilities Act to deal with. Does he have any religious or ethnic beliefs that limit his bathing? If so, then there is Title VII of the 1964 Civil Rights Act to think about.
However, if the problem isn't either of those and the employee in question is just a slob who likes to come to work after 90 minutes of working out without a shower, you can confront this employee.....but exercise tact, diplomacy, and restraint. Personally, I would recommend spending a little time with the employee to see if the problem really is as bad as people say. If so, you MUST communicate that the body odor is affecting the work of those around him. Like the wise man once said, "it's not personal, it's strictly business".