Ronald Stuart Thomas (R S Thomas) (March 29, 1913 - September 25, 2000) was, in his lifetime, the leading Anglo-Welsh poet, known for his cynical and ambivalent attitude towards his own nationality.

Thomas was born in Cardiff and educated at the University College of North Wales, Bangor. Ordained as a clergyman in 1937, he learned the Welsh language in adulthood, and achieved success as a poet only in his forties, with Song at the year's turning (1955), which brought him an audience outside his native land. On the death of his near-contemporary, Dylan Thomas, R.S. effectively took on the mantle of the leader of the poetry scene in Wales. He retired as vicar of Aberdaron in 1978, but continued to write and to be vocal about politics. He was nominated for the Nobel Prize for Literature in 1995, becoming the elder statesman of the Welsh literary scene.