I.R. Baboon (I.R. or Baboon for short) is the deuteragonist of the series. He is the exact opposite of Weasel who he is always trying to top in order to be better than him. He is a baboon who is unintelligent, jealous, ugly, willing to sniff his finger half of the time, and has no talent at most things. I.R. is in possession of a bright red butt that he never wears pants to cover, and therefore is ridiculed for it. He is often depicted doing the opposite of what most would consider sensible. As Weasel has good luck, I.R. seems to have bad luck: for instance, when he was about to get married, his bride fell in love with someone else and left him standing at the altar. I.R. is also the adoptive father of Grampa, a baby who was left on his doorstep in the episode "I.R. Mommy" and I.R. named it after his grandfather, whom he seems to greatly respect. At the end of the episode, Grampa grew up.
I.R. wears a white T-shirt with his short name "I.R." handwritten upside-down on the front of it. He lives in a run-down trailer near Weasel's mansion. I.R. fails to use proper grammar sometimes, explaining the titles for some episodes ("I Are Big Star", "I Are Music Man", "I Are a Artist", "I Are Bellhop", among others), and also refers to himself in third-person. He frequently attempts to outdo Weasel in everything, and when he believes that he has done so, will perform a routine victory dance which consists of putting his hands on his hips and jumping around in a circle while repeatedly chanting a declaration of his success. However, in some episodes, I.R. and Weasel are shown to be friends and partners instead of rivals, such as when they were pilots assisting in an "air-migration" service in the episode "I Am Bush Pilot", or when there were deceased ghosts trying to scare a D-movie actress portrayed by The Red Guy in the episode "I Are Ghost".