Sir Ranulph Twisleton-Wykeham-Fiennes, 3rd Baronet, OBE (born 7 March 1944), usually known as Ranulph (Ran) Fiennes, is a British adventurer and holder of several endurance records. He was the first man to visit both the north and south poles by surface means and the first man to completely cross Antarctica on foot. In May 2009, aged 65, he climbed to the summit of Mount Everest. According to the Guinness Book of World Records he is the greatest living adventurer.

Fiennes was born in Windsor, Berkshire shortly after the death of his father, Lieutenant-Colonel Sir Ranulph Twisleton-Wykeham-Fiennes, who was killed in action in the Second World War at Monte Cassino in 1944. Fiennes inherited his father's baronetcy, becoming the 3rd Baronet at his birth. Fiennes is the third cousin of Hollywood film actors Joseph and Ralph Fiennes, and is a distant cousin of Britain's royal family.

After the war his mother moved the family to South Africa where he remained until he was 12. Ranulph then returned to be educated at Eton, after which he joined the British Army.