The Alphabetrians are a race of aliens who resemble giant letters. Some of them represent different materials. (For example: Water-T - Water, Magma-Q - Magma.) They appeared in the episode "Get Schwifty". The Alphabetrians are rivals with the Numbericons, and in this episode, they were in a war with them. They were defending their planet during the invasion from the Numbericons. Water-T went up against the Numbericons and jumped out into the army and started shooting all of them up.
After Magma-T, Sinistar-7, Mr. Goldenfold, Sulfur-P and Morty Prime defeated Infinity, the Alphabetrians began to live on Alphabetrium with Numbericons.