"Rainbow Monkey Kong" (voiced by Frank Welker) was a giant, real-life Rainbow Monkey that Numbuh 4 encountered on the mysterious Rainbow Monkey Island in Operation: H.U.G.S. after being kidnapped by a group of Rainbow Monkey fan girls. Being a Rainbow Monkey, it was naturally loving and peaceful despite its ferocious appearance and wild nature, which Wally did not approve of and attempted to train the monkey to be feral. This did not work until Numbuh 4 gave up, insulted the monkey and left without giving it a hug, making it very angry and causing it to follow him and attack the Sector V Treehouse. Numbuh 4 was able to calm the giant monkey down by giving him a "friendly friend Rainbow Monkey goodbye hug". When Numbuh 2 and Numbuh 1 teased him, Numbuh 4 denied he hugged the monkey and called it stupid. Unfortunately, the monkey heard him and began to attack him again.
- The creature is based on King Kong.