William Dool Killen (16 April 1806 - 10 January 1902) was a minister of the Presbyterian Church in Ireland and church historian.

Born at Church Street, Ballymena, County Antrim, on 16 April 1806, he was third of four sons and nine children of John Killen (1768-1828), a grocer and seedsman in Ballymena, by his wife Martha, daughter of Jesse Dool, a farmer in Duneane. His paternal grandfather, a farmer at Carnmoney, married Blanche Brice, a descendant of Edward Brice; a brother, James Miller Killen (1815-1879) was a minister in Comber, County Down. Thomas Young Killen Moderator, in 1882, of the General Assembly of the Presbyterian Church in Ireland was his father's great-nephew.

After attending local primary schools, Killen went around 1816 to Ballymena Academy, and in November 1821 entered the collegiate department of the Royal Academical Institution, Belfast, under James Thomson. He was in 1827 licensed to preach by the Presbytery of Ballymena, and on 11 November 1829 ordained minister at Raphoe, County Donegal.

In July 1841 Killen was appointed, by the General Assembly of the Presbyterian Church in Ireland, its professor of church history, ecclesiastical government, and pastoral theology, in succession to James Seaton Reid. He concentrated on history. When Assembly's College, Belfast was set up in 1853, he became one of the professors there. In 1869 he was appointed president of the college, in succession to Henry Cooke, and undertook to fundraise for professorial endowments and new buildings.

In 1889 Killen resigned his chair but continued as president. He died on 10 January 1902, and was buried in Balmoral Cemetery, Belfast, where a monument marked his resting place. He received the degrees of D.D. (1845) and of LL.D. (1901) from the University of Glasgow. His portrait, painted by Richard Hooke, hung in the Gamble Library of the Assembly's College. (wikipedia.org)