On February 1st 1709, after four long years marooned alone, Scottish sailor Alexander Selkirk was rescued from Isla Mas a Tierra, an isolated, uninhabited island off the coast of Chile. Selkirk wasn't shipwrecked; he was put ashore at his own request after a quarrel with his captain. But otherwise, that privateer's adventure bears a significant resemblance to that of the fictional hero Robinson Crusoe. That's probably because Daniel Defoe's castaway character was likely inspired (at least in part) by Alexander Selkirk.
The terms Crusoe (and Robinson Crusoe) occasionally are used to name "a solitary castaway, particularly one who lives or survives by his own unaided effort and ingenuity." And Robinsonade has found a place in literary theory as a designation for "a fictitious narrative of often fantastic adventures in real or imaginary distant places." But undoubtedly, the most common borrowing from Defoe's narrative is the name of Crusoe's fictional servant. Of course, we're talking about Friday.
Robinson Crusoe was published in 1719, but it wasn't until 1887 that man Friday was first spotted in print. Girl Friday and eventually gal Friday followed, and now all three are established bywords for any efficient and devoted aide or employee.