The sandwich (item of food consisting of two pieces of bread with a filling between them) is named after the British statesman John Montagu (1718-92), 4^th Earl of Sandwich.

It is generally said that the sandwich was invented because he once spent twenty-four hours at the gaming-table without other refreshment than some slices of beef placed between slices of toast.

However, this rests on an isolated text, a passage from Londres (Lausanne, 1770), by the French man of letters and travel writer Pierre-Jean Grosley (1718-85). Grosley’s residence in London was in 1765, and he speaks of the noun sandwich as having then lately come into use:

     original text:
Les Anglois profonds, violens, outrés dans toutes leurs passions, portent celle du jeu à l’extrême : on nomme plusieurs lords très-riches qui s’y sont absolument ruinés : d’autres prennent sur les affaires, sur le repos, sur leur santé le temps qu’ils lui donnent. Un ministre d’Etat passa 24 heures dans un jeu public, toujours occupé au point que, pendant ces 24 heures, il ne vécut que de quelques tranches de bœuf grillé, qu’il se faisoit servir entre deux rôties de pain & qu’il mangeoit sans quitter le jeu. Ce nouveau mets prit faveur pendant mon séjour à Londres : on le baptisa du nom du ministre qui l’avoit imaginé, pour économiser le temps.

     literal translation [note 1]:
The English, deep, violent, excessive in all their passions, carry that for gaming to the extreme; several wealthy lords are named whom it brought to absolute ruin; others take from the business, from the rest, from their health the time that they give to it. A Minister of State spent twenty-four hours at a gaming house, always absorbed to such an extent that, during those twenty-four hours, he only lived on some slices of grilled beef, that he got served between two slices of toast and that he ate without quitting the game. This new dish grew in favour during my residence in London; it was named after the minister who invented it, to save time.

In The Insatiable Earl: A Life of John Montagu, 4^th Earl of Sandwich, 1718-1792 (London, 1993), the British historian Nicholas Andrew Martin Rodger (born 1949) explains why he disagrees with Grosley’s account:

There is no supporting evidence for this piece of gossip, and it does not seem very likely that it has any foundation, especially as it refers to 1765, when Sandwich was a Cabinet minister and very busy. There is no doubt, however, that he was the real author of the sandwich, in its original form using salt beef [note 2], of which he was very fond. The alternative explanation is that he invented it to sustain himself at his desk, which seems plausible since we have ample evidence of the long hours he worked from an early start, in an age when dinner was the only substantial meal of the day, and the fashionable hour to dine was four o’clock.

The earliest known occurrence of the noun sandwich is from the journal of the English historian Edward Gibbon (1737-94)—the fact that he used this noun in a way showing that it was already well established in 1762 contradicts Grosley’s affirmation that the sandwich grew in favour during his residence in London in 1765:

(1841 edition)
November 14, 1762. I dined at the Cocoa Tree with Holt, who, under a great appearance of oddity, conceals more real honour, good sense, and even knowledge, than half those who laugh at him. We went thence to the play (The Spanish Friar), and, when it was over, returned to the Cocoa Tree. That respectable body, of which I have the honour to be a member, affords every evening a sight truly English. Twenty or thirty, perhaps, of the first men of the kingdom in point of fashion and fortune, supping at little tables covered with a napkin, in the middle of a coffee-room, upon a bit of cold meat or a sandwich, and drinking a glass of punch. At present we are full of king’s councillors and lords of the bedchamber, who, having jumped into the Ministry, make a very singular medley of their old principles and language with their modern ones.

 

Notes:
 1 A less literal translation is found in A Tour to London; or, New Observations on England and its Inhabitants. By M. Grosley (London, 1772), by the Irish historian and travel writer Thomas Nugent (circa 1700-1772):

The English, who are profound thinkers, violent in their desires, and who carry all their passions to excess, are altogether extravagant in the article of gaming: several rich noblemen are said to have ruined themselves by it: others devote their whole time to it, at the expence [sic] of their business, their repose and their health. A minister of state passed four and twenty hours at a public gaming-table, so absorpt [sic] in play that, during the whole time, he had no subsistence but a bit of beef, between two slices of toasted bread, which he eat [sic] without ever quitting the game. This new dish grew highly in vogue, during my residence in London: it was called by the name of the minister, who invented it.

 2 salt beef: N. A. M. Rodger refers to Thomas Nugent’s translation.