Wererat

A wererat is a fictional creature akin to a werewolf, but shapeshifting into the form of a rat instead of a wolf. This type of therianthrope is rare in historical legends, but has become common in modern role playing games and fantasy fiction inspired by them. They are commonly portrayed as sewer-dwelling scavengers and opportunistic thieves.

Mythology
There are some references to "goblin rats" or rat-themed yōkai in some Japanese myths that may or may not be the source for the wererats in games and novels. Brad Steiger has written about wererat sightings in Oregon, mostly by children. Some of the Benandanti were supposed to change into mice.

Games
In the Dungeons & Dragons fantasy role-playing game, the wererat is one of several different types of animalistic forms. Not lycanthropes, for the word reflects a lupine, or wolven, form, but other transformations of the "were" species. They are also found in various games inspired by or based on Dungeons & Dragons such as NetHack and Neverwinter Nights.

See Ratkin for wererats in White Wolf's "World of Darkness" role-playing setting.

Fiction
Wererats also appear in the Anita Blake: Vampire Hunter series by Laurell K. Hamilton (see wererats in Anita Blake mythology and wererat characters in Anita Blake).

The rats changed into men are characters in the fairy tale Cinderella and star in various adaptations such as the children's book I was a Rat by Philip Pullman.

Yuki Sohma, from a popular manga series, titled Fruits Basket, transforms into a rat when hugged by a member of the opposite gender or when weakened.

Peter Pettigrew is a rat Animagus, akin to a wererat, in the Harry Potter series.

In the American Manga Gold Digger wererats were one of several lycanthropic races created by an enchanter named Iceron. Five characters important to several recent events are wererats. Sherissa, the near immortal leader of the wererat clans, Gothwrain her thrall, servant and apparent enemy, and also three young warriors/assassins collectively known by fans as the Mall Rats (Gold Digger): Lydia McKraken, Romeo Ellis and Moisha Rich.