Frederick William FitzSimons (6 August 1870 Garvagh, Ireland – 25 March 1951 Grahamstown), was an Irish-born South African naturalist, noted as a herpetologist for his research on snakes and their venom, and on the commercial production of anti-venom. FitzSimons emigrated to South Africa in 1881 and was educated in Natal and then returned to Ireland to study medicine and surgery for three years. However, he returned to Pietermaritzburg in 1895 without qualifying.