Sir Algernon Phillips Withiel Thomas KCMG (3 June 1857 – 28 December 1937) was a New Zealand university professor, geologist, biologist and educationalist. He was born in Birkenhead, Cheshire, England in 1857 and died in Auckland, New Zealand in 1937. He is best known for his early research (1880–83) into the life cycle of the sheep liver fluke (Fasciola hepatica), a distinction he shared with the German zoologist Rudolf Leuckart, his report on the eruption of Tarawera (1888) and his contribution to the development of New Zealand pedagogy.