Wakko is the same species as the other Warners and is a little taller than Dot. Wakko is arguably the most animalistic of the trio, as several segments have them behaving like a dog - walking on all fours, doing tricks for treats, etc. They are the only one of the three that wears a shirt and has a red hat, which they keep on even when they do another costume. They also do not wear pants on most occasions, often joking about this aspect.
Wakko is the middle child (in the song "Hello Nurse" they says they're "seven" to rhyme with "heaven," though according to Tom Ruegger, Wakko is actually 11),
and the weirdest and most absurd of the bunch, hence their name. Wakko speaks with a Scouse accent that Harnell explicitly modeled after Ringo Starr (initially Harnell created a John Lennon-esque voice for Wakko until he saw that the character was short, so he just raised the pitch). Wakko often carries a "Gag Bag", from which objects can be produced as needed, and also uses a large mallet when situations call for it. More often than not, their tongue is sticking out of their mouth (it will hang out at any given moment). Wakko generally supplies the more crude humor, which Yakko will often react to. They are the most physical of the three, and thus tends to lean toward physical humor (hence the first syllable in their name being "Wak"). Wakko is very flexible (there are a few episodes where the others make use of Wakko for ladders and measuring tape). Wakko appears to have a voracious appetite in the show, and will eat almost anything, including gum found under a seat and even rocks for shock value or perhaps simply to see how they taste. They also have a fear of clowns. They're a big fan of Don Knotts from The Andy Griffith Show and, like their brother Yakko, they will also hit on any girl despite their young age. Like Yakko, he has a catchphrase: "Faboo!" meaning fabulous or great. Often their siblings use variations of "faboo", as in calling a male antagonist "Dadoo" to annoy them. According to the song "Hello Nurse" Wakko is seven years old; this was the only reference ever made to their age, and was not considered canonical by the writers.
Wakko's trademark is a cap; when the Warners wear costumes, Wakko will usually keep their cap on, which holds Elvis Presley hiding in the cap's hammerspace. Without the cap, Wakko looks very similar to Yakko, as seen in various episodes and the movie Wakko's Wish. They follow in Yakko's footsteps by singing all the fifty US states and their capitals, in "Wakko's America". Wakko is usually the least talkative of the three unless they are the main character, in some segments saying nothing at all. They also appear to be the most musical as well, being able to belch pieces of classical music (under the stage name "The Great Wakkorotti," with Maurice LaMarche providing the belches), play both the violin and the piano, and get behind a drum kit to deliver the occasional sting after a punchline. In the episode, "Chalkboard Bungle", Wakko can impersonate Ray Charles pretty well. Their musical abilities, penchant for physical comedy, and usual quiet attitude seem to reference Harpo Marx.