The love and loyalty of man’s best friend is not something that should be taken for granted. No one recognized this fact better than the Irish. There, the dog (known in Celtic as Cú) was so highly respected, that it was assumed that anyone who, in turn, earned the respect of a dog was worthy of special recognition. The custom developed to award the prefix “Cu” to the name of any warrior or king who proved himself worthy enough to gain the respect and loyalty of a dog.

Source: McBryde, Mary (1998). The Irish Wolfhound: Symbol of Celtic Splendor. John Wiley & Sons. p. 19. ISBN 978-0-87605-169-6.