Each hero has their own tier. Each tier opens up new levels of the hero, abilities and increases their strength.
There are 11 tiers:
Common
- Rare
- Epic
- Legendary
- Mythic
- Supreme
- Ultimate
- Celestial
- Stellar
- Immortal
- Divine
The tier can be increased every 10 levels of the hero (and if you have the required number of cards and gold).