From The Sunday Her­ald:

“Harry Pot­ter has magicked his way into the Eng­lish lan­guage: the word ‘muggle’ is to appear in the Oxford Dic­tion­ary.
Coined by author JK Rowl­ing, the word was ori­gin­ally used in her best­selling Harry Pot­ter series of books to mean a per­son who can­not prac­tise magic. It has since passed into pop­u­lar cul­ture as a way of describ­ing any­one who is clumsy or unable to mas­ter a skill, such as computing. ”

An inter­est­ing art­icle which men­tions some of the his­tory of fic­tional words in the OED. Unfor­tu­nately Toby McDonald’s research is attro­cious! This para­graph:

“Last year the author won a high pro­file legal battle after US-based writer Nancy Stouffer, who wrote the Worst Witch series, claimed Rowl­ing was a pla­gi­ar­ist who had stolen her mater­ial. Stouffer argued the word ‘muggle’, now cred­ited to Rowl­ing, was used by the stu­dent witches in her own fic­tion to the same effect.”

is com­pletely wrong!
Jill Murphy wrote The Worst Witch books. Nancy Stouffer wrote “The Legend Of RAH And The Muggles”.