John Alexander Thynne, 4th Marquess of Bath (1 March 1831 20 April 1896), styled Viscount Weymouth between March and June 1837, was a British diplomat and a peer for almost sixty years.Born in St James's, he was the son of Henry Thynne, 3rd Marquess of Bath and his wife Harriet, second daughter of Alexander Baring, 1st Baron Ashburton. He succeeded his father as Marquess in June 1837, aged only six. Lord Bath was educated at Eton College and Christ Church, Oxford. He was a devout Anglo-Catholic and a determined opponent of the Public Worship Regulation Act 1874 which sought to suppress Ritualism in the Church of England.