English botanist who was largely responsible for establishing the rubber industry in the Malay Peninsula.

After receiving a science degree at Exeter College, Oxford, in 1877, Ridley took a botanical post at the British Museum. He remained there until 1888, when he went to Singapore to take charge of the forest administration of the Straits Settlements and the Botanic Gardens in Singapore. There he conducted experiments with Para rubber trees (Hevea brasiliensis) that convinced him of the enormous economic potential of rubber as a plantation crop. After developing a more efficient tapping method, he began a campaign to establish a rubber industry. Despite considerable initial opposition among planters, he persisted, and by 1896 the first rubber estates were planted using his seeds. From this beginning the rubber industry grew into one of the economic mainstays of the Malay states.

Ridley also carried out an extensive study of plants of the Malay Peninsula, especially monocotyledons, and published many articles as well as a five-volume Flora of the Malay Peninsula (1925). After his retirement in 1912, he spent the remainder of his exceptionally long life continuing research and writing.