Watcyn Thomas (16 January 1906 – 10 August 1977) was a Welsh rugby union player who captained Wales in the early 1930s.
Thomas was born in Llanelli and educated at Llanelli County School and at University College, Swansea. While still at school he was the first captain of the newly formed Welsh Secondary Schools XV in 1924. He then joined Llanelli RFC, moving to Swansea in December 1927. A teacher by profession, he moved to St Helens to teach at Cowley Grammar School in 1929, and played rugby for Waterloo and Lancashire, captaining Lancashire to the championship in 1934-35.
After Llanelli's victory against the touring New Zealand Maoris, he won his first cap for Wales against England in 1927. Against Scotland in 1931 he played for 70 minutes with a broken collarbone and scored a try. As captain he led Wales to victory over England at Twickenham in 1933, overcoming the "Twickenham bogey" that had haunted Wales. However, after the match against Ireland the same year, Thomas fell out with the selectors, who had selected a prop as flanker and a flanker as prop for the match. Thomas ignored this and played them in their usual positions, and never played for Wales again.