Cohen the Barbarian is a character from the Discworld novels. I believe he shows up in The Light Fantastic, Interesting Times, and The Last Hero, and his daughter Conina is a major character in Sourcery.I'm not sure who Cohen the Barbarian is. Does he work at H&R Block? :-D
Cohen is your typical pulp barbarian along the lines of Conan (or at least the popular idea of Conan). He is also somewhere north of 80 years old, with typical problems that come with old age. When asked what is best in life, his reply is "Hot water, good dentishtry, and shoft lavatory paper." But the man has been actively adventuring for a long, long time, and he's very, very, very good at what he does.
Here's a picture of Cohen meeting the main gods of the Disc: