Larry was created as a response to demand from Kids WB executives to include additional characters on the show. His presence is sporadic, as the writers believed that including an additional character would ruin the chemistry between Pinky and Brain - as they worked best as a comedy duo. It was postulated that a third character would, therefore, be out of place, and unnecessary to the plot. It also foreshadows Elmyra being forced into the show in the final season.
He is an obvious parody of Larry of the Three Stooges, given they share similar hair styles. Like his human counterpart, he acts as a middle man between the Brain's intellect and Pinky's stupidity. There's also an original theme song for the group which has Larry's name hastily spliced into key parts of the show's normal theme. For example: "They're Pinky and The Brain (and Larry), yes Pinky and The Brain (and Larry), one is a genius, the other's insane (and the other one's Larry). The recurring theme of this episode is the acknowledgment (or lack thereof) of Larry's existence. This also paralleled many of the Stooges' sketches, wherein Larry is deemed the most underrated of the Three Stooges.
Absolutely no explanation is given for Larry's presence in the episode. Pinky and Brain act as if he had always been there, even though the viewer has never seen him before. Thus, he feels a need to constantly point his existence out. His lines consisted mostly of greetings, and of reminders that he is a part of the episode. At the end of the episode, when the Brain realizes that they don't actually need Larry, Larry decides to change his name to Art (a reference to Art Garfunkel, whose hair is similar to that of the Three Stooge's Larry) and start a new career as a folk singer, singing "The Smells of Loudness" (a parody of The Sounds of Silence) with Paul Simon.
Just as the Brain declares that he and Pinky will continue to attempt to rule the world without Larry, they are almost immediately joined by a mouse named Zeppo (a parody of Zeppo of the Marx Brothers), and the episode's closing song splices in Zeppo's name like it did with Larry in the opening theme. Although never seen onscreen beyond the cameo appearance, Larry is referred to by both Pinky and Brain in subsequent episodes.
Larry was voiced by Billy West, using the same voice as Stimpy from Ren and Stimpy. Rob Paulsen voices him in the opening theme.