Sergio Aragonés is a longtime MAD Magazine artist and co-creator (with Mark Evanier) of Groo the Wanderer, a comic book series for which Stan Sakai is the letterer. Aragonés has made two small contributions to Usagi Yojimbo: the story "Broken Ritual" is based on an idea by Aragonés, and he served as a guest inker for the black and white version of the story "Return to Adachi Plain" that is featured in Book 11: Seasons. He also contributed a pinup to The Art of Usagi Yojimbo: 20th Anniversary Edition and wrote the introduction to Book 7: Gen's Story.
A caricature of Aragonés appears on the cover of Usagi Yojimbo Vol. 1 No. 20.