In the campaign mode, he can only be found in the Irish city of Caiseal. In the sandbox modes, he can be found randomly in any city. In either case, it costs 300 peningas to hire him.
Due to his high agility, athletic and horse riding skill when recruited, he can act as an excellent skirmisher or cavalry unit. In the long term, Ailchu can become a better path finder and spotter than Caio, because Ailchu's agility can be maxed by level 16, which is much sooner than Caio can be maxed in that attribute.