The Latin phrase "E Pluribus Unum" translates to “Out of many, one.” It was the national motto of the United States until replaced in the 1950s by "In God We Trust" and appears on the Great Seal of the United States of America as well as the Seal of the President of the United States.

The phrase has been mandated to appear on every coin struck by the U.S. Mint since an 1873 law. (Not every U.S. coin issued before and after the implementation of the 1873 act bears the motto, though, so some latitude was granted. ) 

According to a 1995 Coin World article by Michael Hodder, the motto’s presence on coinage goes back quite a bit further than that 1873 law.

"Pride of having been the first coinage to display the national motto goes to the 1786 New Jersey state coppers. Their reverse design incorporates the Union shield in the center with E PLURIBUS UNUM inscribed around it,” Hodder writes. "The E PLURIBUS UNUM motto did not appear on federal issue coins until the 1796 quarter eagles. Both varieties of that date, With and Without Obverse Stars, have as their reverse types the arms of the United States. Of course, the eagle on the arms bears a scroll in its beak on which is inscribed E PLURIBUS UNUM.”

The national motto has also appeared on the back of $1 notes since 1935, according to the U.S. Department of the Treasury. 

As for the motto itself, Hodder writes that it likely came from a popular magazine in Great Britain, of all places.

"For many years one of the sayings found on the title page of Gentleman's Magazine was our own motto, E PLURIBUS UNUM. It came from a paraphrase of part of a line from one of the Roman author Virgil's Eclogues, and it originally referred to many bees cooperatively making one sweet product, their honey,” Hodder’s article reads. " E PLURIBUS UNUM appeared on the front of Gentleman's Magazine for many years and it must have become a very familiar sight to the readers of the magazine.”

According to Hodder, Thomas Jefferson, John Adams and Benjamin Franklin — who first suggested in 1776 that the phrase appear on the Great Seal of the United States of North America — would have likely been subscribers. Gentleman's Magazine, founded in London 1731, ran for nearly 200 years.

"Its sentiments, that many different hands can unite to create something sweeter and greater than existed before, would have appealed to their republican ideals,” Hodder writes.

The triumvirate’s seal design was turned down due to its inclusion of the arms of Britain along with those of the other European countries that contributed to North American colonization. However, E PLURIBUS UNUM would appear on the heraldic eagle seal designed by William Barton and Charles Thomson that would be adopted by the Continental Congress in 1782.