On 9 November 1919, Master Tom, a prototype of Felix, debuted in a Paramount Pictures short titled Feline Follies. It was a success, and the studio quickly set to work producing another film featuring Master Tom, Musical Mews (released 16 November 1919). It too proved successful with audiences. According to animator Otto Messmer, it was John King of Paramount Magazine who suggested the name "Felix", after the Latin words felis (cat) and felix (happy). The name was used for the third film starring the character, The Adventures of Felix (released on 14 December 1919).

According to staffers, Felix was based on Charlie Chaplin's Little Tramp character, which Messmer had animated for Pat Sullivan's studio early on, and the down-and-out personality and movements of the cat in Feline Follies do reflect key attributes of Chaplin's character.

In 1958, Joe Oriolo introduced a redesigned, "long-legged" Felix, along with now-familiar elements such as Felix's Magic Bag of Tricks, a satchel that could assume the shape and characteristics of anything Felix wanted.

As Felix became more popular, a handful of co-stars emerged, including Felix's master Willie Jones, a mouse named Skiddoo, Felix's nephews Inky, Dinky, and Winky, and his girlfriend Kitty.

The Professor (real name: Professor Nutty Nut-Meg as seen in his papers) is Felix's archenemy and, in most appearances, is trying to steal the Magic Bag of Tricks, though he always winds up failing in the end. In some episodes, when the professor gives up on his episodic schemes, he laments: "Oh, what's the use!!!!!"

Rock Bottom is a bumbling minion of the Professor. With more brawn than brains, he often takes the Professor's instructions too literally and messes up his boss's schemes.

Poindexter is the Professor's genius nephew with an IQ of 777. He speaks in complicated scientific jargon, but when he is misunderstood (which is often), he can usually sum up the gist of his statement in 3 or 4 simple words.

The Master Cylinder was an evil cyborg that emerged as a major antagonist in the 1960s. In his first appearance, he was defeated by being unplugged. He overcame this weakness by gaining feet and operating with a different power source.

Vavoom is a small, unassuming and friendly Inuit whose only vocalization is an earth-shattering shout of his own name "VAVOOM" (but who is powerless if his mouth is taped shut).

General Clang made his debut in "General Clang and the Secret Rocket Fuel" (1960). The general of strange squid-like soldiers, Clang is himself some kind of giant octopus/squid with an admiral's hat.