I Am Weasel was originally a part of the Cow and Chicken show, often airing as the middle of three segments, in between two Cow and Chicken segments. ("The Ugliest Weenie", a two-part Cow and Chicken story, even made reference to the I Am Weasel cartoon interrupting the storyline.) Eventually, I Am Weasel was spin-off into its own series, airing between 2000 and 2008, with both new episodes and the episodes that had aired on Cow and Chicken included in that series (much like how Pinky and the Brain was spun off from Animaniacs or how Evil Con Carne came from Grim and Evil).
The series usually consists of two anthropomorphic animal characters: I.M. Weasel and I.R. Baboon. Both characters' species are as suggested by their names.
I Am Weasel
I Am Weasel is highly intelligent, and is skilled in most if not all known professions, anything from electronics and engineering to medicine and philosophy; he is also incredibly charming and well-versed in the social graces, and will often have characters such as Loulabelle at his side. Weasel's only real flaw is a secret desire to suck the yolk from eggs (though such behavior is actually a characteristic of the mongoose family). He is usually the only successful character in a given episode. The standard image of Weasel wears no clothing, though he will often don outfits appropriate to his activities (such as a lab coat when working as a doctor or scientist). Weasel will usually call I.R. "Mr. Baboon" instead of "Baboon"; however, in "I.R. Gentlemans," he called I.R. "Monsieur Baboon" and "I.R." in "The Hole". In "Happy Baboon Holidays" Weasel hurt I.R.'s feelings when he took I.R.'s family into his house to thaw out after they got left out in the cold. He is prone to declaring "I Am Weasel!" before leaping into a situation.
Voiced by: Michael Dorn
In contrast, I.R. Baboon is considered dim-witted and slovenly, uses incorrect grammar when he speaks (for example, I.R. stands for "I are"), and is very envious of Weasel's success. He is often shown doing the opposite of what would be considered sensible, and sometimes displays obsessive-compulsive behavior (as in the episode, The Hole, when he was determined to plug up the largest hole in the world). I.R. Baboon has few skills (either social or practical), but was discovered unexpectedly to be a virtuoso on the theremin (apart from the fact that the theremin is faulty and causes earthquakes when it is played). Baboon wears only a T-shirt with a handwritten, upside-down "I. Я." (as suggested in the opening video); his protruding bright red buttocks are often highlighted (as in the episode I Am Terraformer when he wore a spacesuit and there were two separate bubbles on the helmet for his buttocks), and serves as a focus of others' ridicule. He attempts to outdo Weasel at everything, and when he believes he has succeeded, he performs a routine victory dance, placing his hands on his hips and jumping around in a circle while repeatedly chanting a declaration of his success. His antics and victory dances are often accompanied by off-screen frantic monkey noise. In some of the episodes, Weasel and Baboon are actually friends and work together. In the first season he spoke with a French accent, but later on changed his accent.
Voiced by: Charlie Adler
The Red Guy
As in Cow and Chicken, The Red Guy plays a devil-like character and Weasel and Baboon's arch-friend/nemesis, but I Am Weasel also grants him a new catch phrase: "Hello!! It's me!", usually followed by his identity in that particular episode. He didn't make his I Am Weasel debut until Series 2, in the episode, "I.R. Mommy." Red almost always confuses weasel for a squirrel or chipmunk. Red's dad is introduced in a particular episode.
Voiced by: Charlie Adler
Minor and One-off characters
- Loulabelle - Weasel's assistant, who usually dresses as a nurse. Her debut was in the Series 2 episode, "I.R. Mommy." Voiced by: Susan Blakeslee (season 2), Teresa Ganzel (season 3). She was dropped from the show after "Time Weasel" since Cartoon Network declared her a blond stereotype.
- Cow and Chicken characters - Besides the Red Guy, some other characters from Cow & Chicken have made their appearances in I am Weasel since Series 2. These include Cow (and Supercow), Chicken, Flem, Earl, Mom, Dad and Teacher.
- Admiral Bullets - Admiral Bullets is a superior in the Navy, who often relies on Weasel. He made appearances in the episodes, "This Bridge, Not Weasel Bridge" and "I.R. Mommy."
- Baby Grampa - In the episode, "I.R. Mommy," I.R. adopts a child, which he affectionally names "Grampa," after his grandfather. By the end of the episode, he is seen as a grown man donning a t-shirt similar to I.R's, in the way that his name is handwriten upside down.
- Jolly Roger - Jolly Roger is an obese guy in a short-sized sailor suit as he debuted in the episode "Unsinkable I.R.". He appeared officially in season 5.