 The character "Miyamoto Usagi" who appears in several episodes (e.g  in "The Big Brawl" or "The Real World") is a character created and  owned by Stan Sakai, a friend of Peter Laird. There have been  several crossovers in the comic world and Usagi was published by  Fantagraphics Books and Mirage Comics and is currently published by  Dark Horse Comics. The comic book is published under the title  "Usagi Yojimbo".