Four is an algebralian and the main host of BFB, and the host of the non-canon one-episode series, Battle for Permission to Meet 10. Four and their co-host X first appeared in the 2008 video "X Finds Out His Value". They appear to be abstract beings representing real-life numbers, letters, or algebraic variables.

Four exhibits very surreal mannerisms, including being able to deform or mutilate characters, revive them, and screech to stun them (killing them on some occasions).