Every dog has its day

This phrase is recorded as being first uttered by no less a notable as Queen Elizabeth I. As Princess Elizabeth, in a letter to her brother and in response to his request for a picture of her, she wrote:

Notwithstanding, as a dog hath a day, so may I perchance have time to declare it in deeds.

The letter was published by John Strype in Ecclesiastical Memorials, 1550. It appears that Elizabeth was merely quoting what was in her day already a well-known proverb, although no record of it has been found that pre-dates her writing it down.

John Heywood recorded the proverb in the 1562 edition of A Dialogue conteinyng the nomber in effect of all the Prouerbes in the Englishe tongue and Shakespeare used it in Hamlet, 1603: 

Let Hercules himself do what he may,
The cat will mew and dog will have his day.

See Fifteen minutes of fame.

See also: the List of Proverbs.