Hall of Fame is a section that consists of 3 factions and allocates all captains among them. You can enter the Hall of Fame via the Hero's interface by clicking on the 'lion' icon on the left side of the screen.

There are Tenacity, Courage, and Resolve factions. 

Every level of each faction gives you permanent bonuses for your Army. You can upgrade faction levels by upgrading the levels of your captains.

Note that captains can be of different quality: Rare (blue icon), Epic (purple icon), and Legendary (orange icon).