“Look out, everybody, things are about to get awesome!”
Birthday Cat is a persona adopted by CL4P-TP units, encountered in Borderlands: The Pre-Sequel and the Claptastic Voyage DLC. Birthday Cat speaks in a deadpan tone of voice, and makes frequent cat-based puns.
Birthday Cat is first encountered in the Pre-Sequel storyline quest Home Sweet Home, when a CL4P-TP attempts to open the door to Jack's Office. It attempts to trick the door into thinking that Birthday Cat is the person trying to open the door. When that attempt fails, the CL4P-TP unit uses Racist Hot Dog instead.
Later in the Claptastic Voyage DLC, Birthday Cat makes another appearance in Claptrap's own mind (along with Racist Hot Dog) in the missions h4x0rz and l33t h4x0rz, offering the Vault Hunters a repeatable arena mission.
- Both Racist Hot Dog and Birthday Cat appear to be personae available to all CL4P-TP units, since they are found in both the random CL4P-TP unit during Home Sweet Home, and Claptrap himself during the Claptastic Voyage DLC. This implies that CL4P-TP units in general might use personae like this in order to open doors. (See also: Claptrap's Consciousness' successful opening of the door to Security by pretending to be "Tiffany," in the Claptastic Voyage mission File Search.) The personae apparently do have some autonomy, though.