A Fighter is a robust unit specializing in axes. They tend to have high HP and strength, moderate speed, but with poor defense. They are present in all games in the series.
Fighters are Axe-Wielders and are very good at destroying enemy units. They have the ability to kill enemies in a instant and do massive damage to bosses. Their main weakness is that due to their low Defense, they will get beat up a lot so it's not a good idea to send a Fighter into a swarm of enemies hoping to clear the field because that will just result in your fighter getting killed. The best strategy to use with Fighters is to use them as tanks alongside other characters such as Cavaliers and Knights and have a Valkyrie, Sage, or Bishop, standing by so your Fighters can get healed if they get too beat up. But even with that, using fighters is risky and painful.
Ben is the first fighter that joins, and is a very powerful force even if others are promoting. Nick joins in chapter 8, followed by Adam in chapter 14. The Warriors Joey and Aeso were presumed to be Fighters before being promoted.