It was story man Izzy Klein who originally had the idea of an insignificant animal with Superman-like powers, and he proposed "Super Fly" at a
a high rates of speed and save others…
… Terrytoons story conference early in 1942. But studio boss Paul Terry, who is said to have liked ideas best when he could take credit for them himself, nixed that one. Shortly thereafter, Terry came up with the same thing, except with a mouse instead of a fly, and "Super Mouse" was born. His first appearance was in The Mouse of Tomorrow, released Oct. 16 of that year. Before it even hit theaters, the second, Frankenstein's Cat, was in production, for release on November 27. By that time, the character was already being used to promote non-series Terrytoons releases, appearing with Gandy Goose on the poster for Ickle Meets Pickle.
Even before the Terrytoons character's initial release, however, another character named Supermouse was in the works. October, 1942 was also the cover date of the first issue of Coo Coo Comics, published by Nedor Publishing Co., but in the usual manner of comic books, it's likely to have gone on sale a couple of months earlier. That comic contained a completely different hero, one that Nedor and its successors, Standard Comics and Pines Comics, continued to publish regularly until 1958. Seeing no reason to promote another company's product, in 1943, Terry changed the name of his character to Mighty Mouse, the name by which he is known today. The 1942 and '43 releases were altered in rerelease to reflect the change.
Mighty Mouse went on to become the studio's most valuable property. In part, this was due to a decision to team him with an earlier Terrytoons character, Oil Can Harry, the villain in a brief and unjustly forgotten series of "Mellerdramas" the studio did in the late 1930s. What made these stand out was that they were done in opera style, with dialog sung rather than spoken. Mighty Mouse replaced the earlier hero, Strongheart, in Harry's revival, and Harry was re-designed as a cat. The first opera-style Mighty Mouse cartoon was Mighty Mouse & the Pirates, released January 12, 1945. Aside from Harry, Mighty Mouse's only ongoing supporting characters were Pearl Pureheart (no relation), who played the female lead in these latter-day Mellerdramas, and Mitzi, Mighty's rescue object before Pearl and Harry came on the scene.
It was also in 1945 that he joined the cast of Terrytoons Comics, which at the time was published by the company that would eventually become Marvel. He remained a mainstay of that series through two changes of title and four changes of publisher, until it ended at Gold Key in 1963. He first appeared in his own comic in 1946, and was published steadily all through the 1950s and part of the '60s. The most recent Mighty Mouse comic book series, also from Marvel, appeared in 1990-91.
A third 1945 milestone for Mighty Mouse was his first and only Oscar nomination. Gypsy Life, directed by Connie Rasinski, was the third of four Terrytoons to achieve that distinction. (The first two, All Out for "V" (1942, directed by Mannie Davis) and My Boy Johnny (1944, directed by Eddie Donnelly) contained no continuing characters.)
In 1955, Paul Terry sold his studio to CBS, and Gene Deitch, late of UPA (the studio that was famous for Gerald McBoing-Boing and Mr. Magoo), was brought in to head it. Deitch scrapped Mighty Mouse along with Dinky Duck, The Terry Bears, and all the other old series, and started fresh with such characters as John Doormat and Sidney the Elephant. When Deitch left, in 1958, only Mighty Mouse and Heckle & Jeckle were brought back — but with the already thin Terrytoons budgets slashed to the bone, they were mere shadows of their former selves.
CBS packaged the old Mighty Mouse cartoons, along with non-series Terrytoons, as a Saturday morning half-hour, under the name Mighty Mouse Playhouse. It ran as a network show from 1955-67. Afterward, they dropped the "Terrytoons Classics" segments, added two new ones, "Luno" (about a time-traveling horse) and "The Mighty Heroes" (a superhero parody even broader than Mighty Mouse), and syndicated it.
Mighty Mouse was back with new animation in 1979, when CBS commissioned Filmation (Fat Albert, He-Man) to produce a new Saturday morning series. But even in the darkest days of his theatrical release, the late '50s, Mighty Mouse had never been animated as cheaply as Filmation did him. The show sank after only 16 episodes.