anon12086 says "it has recently been discovered that all through the animation the lettering is by Pat Sullivan". This is not true. It has been claimed that the lettering is by Sullivan, but on very little evidence. A few vague similarities have been stressed, but the most notable feature of Sullivan's handlettering, the convex curves on the letter "A" is entirely absent from the lettering in the films: when not absolutely straight, there is a tendency to the concave on the right hand side of the "A." For myself. I take this as very strong evidence that it is not Sullivan's hand on any of the lettering in the drawings.
Pat Sullivan had been assisting William Marriner on a strip featuring an afro american boy ("Sambo and his Funny Noises" - cringe making title! – featuring a black kid who, although drawn as a typical stereotype of the period, was an engagingly entrepreneurial boy whose schemes comically backfired. The white kids in the strip were either coerced into being his assistants, or stood back and laughed when things went wrong, but Sambo was definitely the prime mover of the strip). When Marriner died in 1914, Sullivan joined Raoul Barre's animation studio and in 1916 started his own animation studio to make a series based on the "Sambo" strip. ("Sammy Johnson", a version of the character's real name in the strip.)
In order to get some help, he hired other animators, including Otto Messmer - who actually got a credit for a Sullivan Studios film called "Chestnuts" (1916) which was a series of single panel cartoons (culled from old magazines) with some animated elements.
In March 1917, Sullivan's studio released a cartoon called "The Tail of Thomas Kat," in which a cat loses his tail to a determined chicken, and is mocked by a dog, but when the dog has a tin can tied to his tail, the cat sees that being tailless has its advantages.
Sullivan's studio released 22 cartoons that year, many of which were credited to other animators. So it is quite possible that Sullivan could have animated this film. No copy is known to exist so we have no way of knowing what the cat looked like.
This is the only Sullivan Studios cartoon to feature a cat as the central character until "Feline Follies"(1919). A few featured dogs, but most centered on human characters.
In the autumn of 1917, Sullivan was jailed for nine months (alleged rape of an underage girl) and the studio closed. It reopened on his release in 1918, with Messmer as chief animator, starting a series based on a cartoon caricature of Charlie Chaplin, just named "Charlie", as no permission had been sought to use Chaplin’s likeness. Sullivan now concentrated on the managerial and promotional side of the business, as it was important to re-establish distribution for his product.
There is no reason to doubt that Sullivan assigned Messmer to make "Feline Follies"; we cannot tell whether or not he suggested the subject matter.
That the cat in "Feline Follies", named as "Master Tom", was based on "The Tail of Thomas Cat" is unlikely. Too much time and too many other film had flowed under the bridge by then. Calling a tom cat "Thomas" is hardly original, which is why, when Sullivan realised he had a new starring character in his stable, he renamed him Felix.
It is certainly true Messmer developed all the mannerisms that personified Felix - the surreal use of his tail as a prop (along with anything else handy on screen!) and especially his trademark pacing up and down while deep in thought. (It may be noted that none of these traits actually occur in "Feline Follies." The success of this film initiated the "cat" series, but his character was as yet undeveloped.)
By Felix's heyday in the 20s, Sullivan had given up animating altogether, in order to focus on running the studio, promoting his films and doing marketing deals.
Although Messmer's claims came after Sullivan's untimely death, they were supported rather than refuted by other animators from Sullivan's studio.
Doubtless, Messmer had exaggerated his case a little - one person's view is always slightly distorted - but against that Sullivan's claims to have created Felix were made purely for the sake of promotion. (And quite rightly too - it was his studio, and Felix was his big star. It was important that the public associated Felix with the studio head.)
It is a pity that Sullivan’s supporters have tried to claim him as the true animator of the early Felix films, which is demonstrably not the case, instead of researching his true part in the nurturing and exploitation of his star property. Without proper marketing, Messmer’s work might never have reached a wide audience, and the name of "Felix the Cat" might never have resonated round the globe.