William Jenkyn Thomas (5 July 1870 – 14 March 1959) was a Welsh headmaster and author best known for his The Welsh Fairy Book. He was an undergraduate student at the University of Cambridge and in addition to his writings worked as a lecturer and teacher. He was the first Head Master at Aberdare Intermediate School (1896-1905) and was headmaster (1905-1935) at Hackney Downs School.
His father, John Thomas, later lived in Cloddia, Llidiardau, Llanycil, on the outskirts of Bala, Merionethshire, and Jenkyn’s family are buried in the Methodist chapel there.