X is an algebralian, variable and the co-host of BFB. They were the host after Donut resigned until Four's return.

X's first appearance in BFB was in "Getting Teardrop to Talk" where they and Four started a competition to win "a BFDI" (a compilation of all season 1 and 2 episodes of BFDI and BFDIA) until BFB 16, where Four's show split into two. X was the co host for TPOT until X Marks the Spot.

X also appears in TPOT with Four as the chefs for the Hotel, with Clock helping them out as of TPOT