What is a fighter? You can answer that question as simply as asking it, but you never really feel satisfied. Fighters are supposed to encompass the way of the warrior, those who live and die by the sword, the monsters who burn villages to the ground and even the humble samurai on bent knee before his charge. So when you ask "what is a fighter?" just understand that the question is what needs to change, not the answer.
This great guide won't tell you everything you need to play a great fighter, but it will help you to get started.