As we all know, werewolves are humans that are transformed into ravenous flesh eating monsters. Some are sentient, but most appear to be feral hunters of humans. Is there such a thing as reverse Lycanthropy? If so, what is the first story of an animal cyclicly turning into a human similar to the way humans turn into werewolves? I'm looking for the earliest example from the movies, TV, books, comics, or legends.
Likely not what you're looking for, but the nature of "first appearance" questions typically warrants this token "ancient legend" response:
I can't give an accurate date, but these stories are typically over 1000 years old, for fun. Most are likely 2000 or more years old.
In many ancient Asian legends there are stories of animals that, after meeting some condition, are able to transform into humans for periods of time.
The most common, is the fox. The "Huli Jing" or "Kitsune" (Chinese or Japanese respectively) is sometimes described as a demon fox, or fox spirit, or a fox that has lived 100 years. Make no mistake, this is no "god that takes the form of a fox" or anything, this is literally a fox that "gains a spirit, or becomes one, after living 100 years".
These foxes can transform into humans for a time, and often take the form of beautiful women, hoping to seduce a man and (in some cases) take his heart or liver. Some stories say that after eating 100 hearts/livers the fox can become a human permanently. The fox myth is all over the place stretching through many nations. This fits best with the notion of cyclic transformation, as the fox is technically unable to stay human and is "cursed/gifted" with human form. The restrictions on this are usually never clearly stated, as the stories written from the perspective of the fox are typically ones that show the fox as benevolent and having fallen in love with some person, but cursed to be a fox. Often they can't stay human simply because it uses too much energy.
A second example is the White Snake. The specific story of Madame White Snake (published in 1620, but existed in oral form for centuries) states that a thousand year old white snake fell in love with a man and transformed herself into a woman to win him. Her goal was not to become human, but instead a goddess through doing good deeds. This isn't a cyclic transformation though.
A third example is that of the Bakeneko. A cat that has lived for 100 years, or simply grew too heavy, may become a Bakeneko. This cat can transform into a "cat-monster" by night where it: takes the form of a human, can re-animate corpses, throw fireballs, and, of course, kill/eat people.
There are many others, often paired with the "if the animal lives 100 years, this happens". Some other examples are: badgers, raccoon-dogs, sea serpents, and seals.
In the Terry Pratchett Discworld Novel Reaper Man, the character Lupine is a wolf who, under the full moon, turns into a wolf-man.
If you count role playing games, then yes. Both the 1st Edition of Dungeons and Dragons and in more recent versions, there were creatures known as wolfweres. These were wolves that gained the ability to turn into humans. I don't know if they have any precedent in lore before that time.
In The Harry Dresden series, there is a book where a character is actually a wolf who takes human form by choice.
In Fool Moon, Tera advises the Alphas, whom she met via the Northwest Passage Project, and agreed to teach them the ways of being a wolf. At the end of Fool Moon, she left civilization for the wilderness. She was implied to be a wolf who could transform into a human, the opposite of a werewolf. One of the possible clues was that Harry Dresden could not Soulgaze her. Source: http://dresdenfiles.wikia.com/wiki/Tera_West
We have an accepted answer which is definitely older, but for future querents, I want to mention Peter David's 1989 novel, Howling Mad, features a wolf bitten by a werewolf who's cursed to turn human under the full moon. It's a romance novel, of sorts.