Plankton is a small white rat owned by Jos & Melba Scatterhorn. Plankton liked biscuits a lot. After Plankton's death August Catcher stuffed him and preserved him with the Elixir of Life.
The Museum's Secret[]
Tom first met Plankton as Melba's annoying pet rat. Don Gervase then stole him and killed him to find the real Elixir; after being revived plankton escaped and somewhow ended up back at the Scatterhorn Museum.
The Hidden World[]
Plankton appeared as a cameo when Tom visited the museum again.
The Forgotten Echo[]
In the far future, as Plankton's head was stuffed with a novel about the best escape techniques which helped Tom escape from the Asylum.