There are currently 58 playable Champions which a Summoner can use to defeat opponents. Characters come in one of five tiers (signified by stars) and are obtained through crystals or via the Versus Arenas. Each Champion has a Hero Rating that you will be able to increase by ranking up, leveling up, Mastery points and in Arenas and Quests through the Synergy Bonuses.
Each character is also assigned to one of six classes, these are Cosmic, Tech, Mutant, Skill, Science and Mystic.