Robert Caldwell was born in Clady, County Londonderry of Scottish parents and was educated at the University of Glasgow. In 1837 he sailed for Madras (landing on 8 January, 1838) as a Presbyterian missionary on behalf of the London Missionary Society and subsequently the Society for the Propagation of the Gospel. During this period, stimulated by his missionary impulse on the one hand, and his keen interest in comparative linguistics on the other, he translated the Bible and the Book of Common Prayer into Tamil. Caldwell wrote a great deal on Indian history and Indian languages, and in 1856 published a landmark work, A comparative grammar of the Dravidian, or, South-Indian family of languages, which established this broad group of mainly southern Indian languages as a major language group of non-indo-European origin. He was consecrated Bishop of Tinnevelly (today Tirunelveli, in Tamil Nadu) in 1877.
Caldwell also immersed himself in the history of the region round Tirunelveli and in 1881 the government of Madras published his book, A Political and General History of the District of Tinnevely; he published a number of works on Christianity and Hunduism, on evangelisation, and on his own life in Madras.
In 1844 he married Eliza Mault (1822–99), daughter of the London Missionary Society's Reverend Charles Mault (1791–1858); she too was involved in missionary work, particularly among Tamil-speaking women. The couple had seven children.
Caldwell died at Kodaikanal in 1891.
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