Every dog has its day

What's the meaning of the phrase 'Every dog has its day'?

Every dog, and by implication every person, has a period of power or influence.

What's the origin of the phrase '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 Proverbs and Epigrams 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.