Who is Cohen the Barbarian from The Light Fantastic and what is their importance?

Cohen is one of Discworld's foremost heroes. However, in the novel he is now in his seventies and not quite the warrior he once was. Nevertheless, he has enough left to save Rincewind and Twoflower on a number of occasions and often by fighting dirty. Cohen falls in love with the much younger Bethen, and they decide to get married.