David Alfred Thomas, 1st Viscount Rhondda, PC, was a Welsh industrialist and Liberal politician. He was UK Member of Parliament (MP) for Merthyr Tydfil from 1888 until the January 1910 general election, then MP for Cardiff until the December 1910 general election, when he left politics to concentrate on his business interests. He was made a member of the Privy Council in 1916. He later held office, notably as "Food Controller" in Lloyd George's wartime coalition government.

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.