Sir Ifor Williams, FBA (16 April 1881 – 4 November 1965) was a Welsh scholar who laid the foundations for the academic study of Old Welsh, particularly early Welsh poetry.
Ifor Williams was born at Pendinas, Tregarth near Bangor, Wales the son of John Williams, a quarryman, and his wife Jane. His maternal grandfather, Hugh Derfel Hughes, was a noted local historian who wrote a well-regarded book on the history of the area. He went to Friars School, Bangor, in 1894 but had only been there for just over a year when he suffered a serious accident. This left him with back injuries that made him bedridden for several years.
Having recovered, he attended Clynnog School in 1901 and in 1902 won a scholarship to the Bangor University. In 1905 he graduated with honours in Greek, then in 1906 in Welsh. He spent the 1906–07 academic year at the Department of Welsh working for his M.A. degree and assisting Sir John Morris-Jones, the Professor of Welsh, before being appointed an assistant lecturer. In 1920 a Chair of Welsh Literature was specially created for him, which he held until Sir John Morris-Jones died in 1929, when he became Professor of Welsh Language and Literature.
Ifor Williams had a lifelong interest in Welsh place-names, and was one of the first to apply rigorous academic methods to this field. He published Enwau Lleoedd ("Place Names") in 1945 which is still of great value today. Many of his early publications were written in order to provide teaching material and included versions with detailed notes of a number of old Welsh tales, notably the Mabinogi in 1930. He also produced books giving the text with notes of the works of a number of mediaeval poets such as Dafydd ap Gwilym and others in 1914 and Iolo Goch in 1925 with colleagues.