Dick Whittington and His Cat

Good old Dick Whittington! He went from his hometown of Gloucester with his cat to London Town to find his fortune, as he heard the streets were paved with gold! Of course, that quickly proved to be horseshit, and he was so disheartened he was ready to leave. but suddenly, he heard the bells of London call out "Turn again, Whittington, thrice Lord Mayor of London!". He decided to stick it through, and after some adventures in Tonga, where his cat killed all the rats in that country, he was given three chests filled with gold, and became Lord Mayor of London! All British people know the story of Dick Whittington!

... except they don't.

Richard Whittington was indeed Lord Mayor of London. In fact, he was elected four times, a feat nobody has ever equalled before or since. During his reign, he made many beneficial changes to the city, such building as a ward for unmarried mothers at St Thomas' Hospital and passing a law prohibiting the washing of animal skins by apprentices in the River Thames in cold, wet weather because many young boys had died through hypothermia or in the strong river currents.. He was also London's sheriff, and a Member of Parliament. And no, he never owned a cat.

The version in the first paragraph i.e. the one everyone in Britain believes is true, started as a play The History of Richard Whittington, of his lowe byrth, his great fortune, and eventually turned into a Pantomime, where equal measures of Adaptation Decay, Critical Research Failure and Memetic Badass has set in quite thoroughly.

Tropes in the fairy tale and the pantomime "Dick Whittington and His Cat":

 * Broken Aesop: Supposedly the story's moral is that success eventually comes to those that don't give up; but Dick Whittington's fortune is more the result of a lucky strike than than the hard work he does as a scullery boy.
 * City of Gold: Supposedly, 'the streets of London are paved with gold' (except they aren't).
 * Prophecies Are Always Right: The bells were right.
 * Rags to Riches: The main motif.
 * Swarm of Rats: The land of the King of Barbary is overrun with mice.