A small spider-like creature kept as a pet by Harry Mudd in a Klingon prison cell in 2256, which he uses to pilfer food and which he fusses over more than his cellmates.
Stuart appears in Choose Your Pain. When Captain Lorca is captured and thrown into a cell aboard a Klingon prison ship, he finds Mudd already there with a many-legged bug that scuttles about the cell and returns to its owner's shoulder.
Mudd talks to Stuart as to a friend and sends him to snatch scraps of food from the other prisoners. The creature is one of the comic touches that introduce this younger version of the trader, though Lorca soon works out that Mudd is also passing information to the guards.
When Lorca and Ash Tyler break out they leave Mudd behind, shouting after them, and Stuart is not seen again.