Alexander Selkirk (1676 – 13 December 1721) was a Scottish privateer and Royal Navy officer who spent four years and four months as a castaway (1704–1709) after being marooned by his captain, initially at his request, on an uninhabited island in the South Pacific Ocean. He survived that ordeal, but succumbed to tropical illness years later while serving aboard HMS Weymouth off West Africa.

Selkirk was an unruly youth, and joined buccaneering voyages to the South Pacific during the War of the Spanish Succession. One such expedition was on Cinque Ports, captained by Thomas Stradling under the overall command of William Dampier. Stradling's ship stopped to resupply at the uninhabited Juan Fernández Islands, west of South America, and Selkirk judged correctly that the craft was unseaworthy and asked to be left there. Selkirk's suspicions were soon justified, as Cinque Ports foundered near Malpelo Island 400 km (250 mi) from the coast of what is now Colombia.

By the time he was eventually rescued by English privateer Woodes Rogers, who was accompanied by Dampier, Selkirk had become adept at hunting and making use of the resources that he found on the island. His story of survival was widely publicised after his return to England, becoming one of the sources of inspiration for writer Daniel Defoe's fictional character Robinson Crusoe.