Heros play important NPC's in evony the 3 stats: politics,attack and intelligence are important.

Politics increase resource production as a major and also shortens construction time.
Attack:increases army attack when assaulting valleys or cities
Intelegence:decrease research time if Mayjor increase information gained in scouting missions.

Its good to find lower leveld heros with a specific high astribute as they level up faster. Heros as Mayjor gain experience over time.
Hope this helps.