Alexander Buchan (died 17 April 1769) was the Scottish landscape artist aboard HMS Endeavour on James Cook's first voyage to the Pacific in 1768, having been appointed to the position by Joseph Banks. His best-known works are his illustrations of the people of western Tierra del Fuego, made during a stopover at the Bay of Success. Banks recorded in his journal that Buchan suffered from an epileptic seizure. He died at Matavai Bay on 17 April 1769, and was buried at sea.
Following his death, Banks took possession of all his drawings. Nearly all of these are currently housed at the British Library, except for several illustrations of south Atlantic marine life held by the Natural History Museum. All surviving works are fully catalogued in The art of Captain Cook's voyages by Rüdiger Joppien and Bernard Smith.