Pinky, as well as Brain, is a white mouse who is being kept as part of Acme Labs' experimentation. They have undergone significant genetic alteration; as per the show's title lyrics, "their genes have been spliced" which gives the two mice amplified intelligence over that of a typical mouse.
Pinky is another genetically modified mouse who shares the same cage as The Brain at Acme Labs. Pinky's personality is described that he is more open-minded and he is much more dim. He speaks with an exaggerated cockney accent. He has several verbal tics, such as "narf", "zort", "poit", and "troz" (the last of which he started saying after noticing it was "zort in the mirror").
Pinky has a straight tail, blue eyes, and a severe overbite, and is taller than the Brain.
Pinky's name was given to him by Brain, thinking that Brain was calling him when in fact Brain was referring to his own pinky digit, when insulting some scientists while talking to himself.