There was a curious belief that the cats of the Isle of Man had a king of their own who lived as an ordinary house-cat during the day but at night assumed his regal powers, and sometimes called together all the cats in a kind of Cat Tynwald.
If anyone was seen ill-treating a cat, such as a farm boy giving one a kick, he was often told “Be careful! That one might be the King of the Cats!”
(source: ‘This is Ellan Vannin Again: Folklore’ by Mona Douglas; artwork by Tokuhiro Kawai)