Stephen Owen Davies, generally known as S. O. Davies, was a Welsh miner, trade union official and Labour Party politician, who served as the Member of Parliament (MP) for Merthyr Tydfil from 1950 to 1972, and previously Merthyr from 1934 to 1950. In 1970, when well past 80, he was deselected as parliamentary candidate by his local party association on account of his age. He fought the constituency in the 1970 general election as an Independent and won comfortably, a rare example in British politics of an independent candidate defeating a major party's organisation.

Merthyr Tydfil was a parliamentary constituency centred on the town of Merthyr Tydfil in Glamorgan. From 1832 to 1868 it returned one Member of Parliament (MP) to the House of Commons of the Parliament of the United Kingdom, and in 1868 this was increased to two members. The two-member constituency was abolished for the 1918 general election.