Alexander Dalrymple FRS (24 July 1737 – 19 June 1808) was a Scottish geographer and the first Hydrographer of the British Admiralty.

He is the main proponent of the theory that there exists a vast undiscovered continent in the South Pacific, Terra Australis Incognita.

He produces thousands of nautical charts, mapping a remarkable number of seas and oceans for the first time, and contributing significantly to the safety of shipping.

His theories prompt a number of expeditions in search of this mythical land, until James Cook's second journey (1772–1775) leads to the conclusion that, if it does exist, it is further south than the 65° line of latitude South.