The other voice actors with whom Sam records a session are played by some of the best-known voice actors in America. Billy West has played various Looney Tunes characters, as well as multiple voices on Futurama (Fry / Dr. Zoidberg / Professor Farnsworth, etc.) and both Ren and Stimpy on Ren & Stimpy. Tom Kenny has performed hundreds of voices for animated works; his most famous character is SpongeBob SquarePants.
Robin is played by Henry Thomas, known for playing the protagonist child, Elliott, in E.T