Skipper (voiced by Tom McGrath) is the leader of the penguins, who forms tactics and gives orders. While usually cool-headed and calculating, he is shown to have a secret fear of needles.
Kowalski (voiced by Jeff Glen Bennett) acts as the group strategist and gadgeteer. While intelligent, Kowalski tends to over-analyze situations.
Private (voiced by James Patrick Stuart) is the emotionally sensitive rookie of the group, who has a knack for cracking codes. He is a nice, sweet-voiced Penguin that has a tendency to care for eggs as normal male Penguins are supposed to. He likes to be the only one to be called Private.
Private
Rico (voiced by John DiMaggio) is the team's weapons and explosives specialist, who communicates through grunts and squeals. Rico swallows useful tools, such as dynamite, and regurgitates them when needed.
Lemurs
King Julien (voiced by Danny Jacobs), is a Ring-Tailed lemur and the self-proclaimed lemur king. Julien is a stuck-up character who has little regard for his "subjects", Maurice and Mort. He has a tendency to use malapropisms and misintepret figures of speech.
Maurice (voiced by Kevin Michael Richardson) is an Aye-aye lemur, and one of Julien's subjects. Though Maurice accepts his life as a servant, he often shows disdain towards Julien and his hare-brained ideas.
Mort (voiced by Andy Richter) is an accident-prone mouse lemur. Unlike Maurice, Mort is fiercely devoted to Julien, even displaying an obsession with the lemur king's feet. However, Julien treats him with contempt.
Marlene (voiced by Nicole Sullivan) is a female otter who was transferred to the Central Park Zoo from an aquarium in California. She is close friends with Skipper and sometimes tags along on his missions, but she believes the penguins are insane.
Mason (voiced by Conrad Vernon) and Phil are two intelligent chimpanzees. Mason can speak but cannot read; Phil is mute but is an avid reader. Phil communicates through sign language which is interpreted by Mason and spoken out.
Alice (voiced by Mary Sherar) is a surly zookeeper. Though another worker can be heard on her walkie-talkie, she is the only one ever seen.
Other minor and recurring characters
The King Rat (voiced by Diedrich Bader) is a transformed, now muscular, lab-rat that often starts fights with the penguins. He lives in a sewer with many other rats, and was first seen in "Crown Fools." He might find birds inferior since he usually calls the penguins "birds" instead of specifically calling them "penguins".
Max the Alley Cat (voiced by Wayne Knight) is a beat-up cat that has a life apparently going nowhere. He was first going to eat the penguins, but became friends with them after they give him some fish: one of his best meals.
Roger (voiced by Richard Kind) is an alligator who lives in a sewer. He was formerly thought by Marlene to be a ghost.
Manfriedi and Johnson were two of Skippers closest friends who never appear onscreen because, according to Skipper, they were killed by a fleet of flying piranha, and Skipper "buried what was left of them with a teaspoon". They, according to Skipper, were optimistic and very naive.
Fred the Squirrel is a really dumb squirrel who takes everything literally and lives in Central Park
Mother Duck and The Baby Ducks are a trio ducks that live in The Otter Exhibit
Dr. Blowhole, another unseen character (but will be seen in an upcoming episode), is a Mad Scientist Dolphin and Skipper's arch nemesis. He once, apparently, had a sinister plot to extinguish the Sun (this was revealed during a solar eclipse, the occurrence of which led Skipper to believe that "he's finally done it".)
Rhonda (voiced by Kathy Kinney) is a disgusting, obnoxious, 1,500 pounds (680 kg) walrus, and a mutant spy working for Dr. Blowhole. In "Roomies", she becomes Marlene's new room-mate, and continues to disgust her to no end. As it turns out, the whole thing was just a ruse so Rhonda could steal Kowalski's "top secret invention" which he "has no idea what it does".
