BGWJJILLIGKKK is described by Merlin as "the most potent spirit known to the magicians of the East, and whose name none may utter and live." in A Connecticut Yankee in King Arthur's Court. This dubious claim is shortly refuted by the Yankee who goes on to utter the following :
...thereafter condemning said spirit to lie bound a thousand years in the pit, commanding him by his own dread name BGWJJILLIGKKK.
Merlin admits, afterward, that the spirit's own mother could not have pronounced it better.