All the playable characters:
 Starting Characters
The four main knights the game start's you out with. They each are a different attribute and have a different play style:
 Unlockable Characters
These characters are unlockable through beating the game with one of the starting knights. With that unlocked character, you can beat the game with him to get another character:
These characters are unlocked by beating the arena's throughout the map. There are 5 arena's that unlock 1 character each. Beating the game with that character will unlock another character (Except the Conehead) :
 Downloadable Content Characters
These characters can only be obtained if you buy the DLC packs. To obtain the Alien you must own the game, "Alien Hominid HD" and get at least 1 achievement from it. Though in the PS3 version, the Alien is unlocked by completing the "Alien Ship" level, and the rest of these characters are unlocked by completing certain levels on insane.