Mad Madam Mim is a fictional witch, best known from the Disney movie based on The Sword in the Stone by T. H. White.
In order to rescue Arthur from her clutches, Merlin challenges her to a sorcerous duel in which the combatants transform into various animals. The duel, a highlight of the movie, is nearly won by Mim when she transforms into a dragon, but Merlin makes use of his future knowledge and transforms himself into a bacterium that carries a terrible disease, making Mim too ill to continue.
It is easy to gain the impression that Mim originated with the movie, as White published several different versions of his novel over the course of his life and the final version of the text does not mention her at all; but she is there to be found in earlier editions, magical duel with Merlin and all.
The Disney version of the character was adopted into the Donald Duck Universe where she sometimes teams up with Magica De Spell and/or The Beagle Boys.
She sometimes appeared in the Mickey Mouse Universe where she teamed up with Black Pete on occasion and she even teamed up with The Phantom Blot at one point. In some European Disney comics, she is a good character.
