Dillon, Wentworth (1637–85), 4th earl of Roscommon , poet, was born (probably in Ireland) in October 1637, only son of James Dillon, 3rd earl of Roscommon, who had been converted to protestantism by James Ussher (qv). His mother Elizabeth was sister of Thomas Wentworth (qv), lord deputy of Ireland from 1633. The boy was sent to Wentworth's house in Yorkshire to be educated, but on his uncle's fall from power he was taken on Ussher's advice to the protestant academy at Caen, northern France. There, it is said, he knew by second sight of the death of his father (October 1649) a fortnight before the news arrived from Ireland. He travelled widely in Europe, especially in Italy, until after the restoration of Charles II, when he returned to England. His estates and titles were restored by an act of the English parliament (December 1660). Roscommon petitioned the king for some recompense for the huge sums of money lost by his family in supporting the royalist cause, but – except for being made captain of the band of gentlemen pensioners – may not have received much compensation. He took his seat by proxy in the Irish parliament on 10 July 1661.
Roscommon travelled to Ireland in 1662 to settle a dispute with the lord privy seal over his estates; while there, he was made a captain in the Irish guards by the lord lieutenant, James Butler (qv), 1st duke of Ormond. He took an active part in the Irish parliament and privy council, but also continued the gambling and duelling for which he had become notorious at the royal court in Whitehall. Leaving the gambling table late one night, he was attacked by would-be assassins; Roscommon killed one unaided, and another with the assistance of a passing gentleman. In gratitude to his new-found friend, he gave up for him his captaincy in the Irish guards. On at least two occasions Ormond intervened to prevent his duelling, in one instance in 1667 ordering his confinement for a night when Roscommon was challenged by the earl of Donegall's son.
Having raised an infantry regiment to fight with the French against the Dutch, he left Ireland in 1671, but returned to Ireland a year later, his regiment having been disbanded by the French. He went to London in 1674 and and was made master of horse to the duchess of York. Turning away from his wastrel lifestyle, he became acquainted with John Dryden and his circle. With them he projected an academy of letters, which met on a few occasions, and where he made a name for himself by translating French and Latin verse, especially a Virgilian eclogue and works by Horace. He published Horace's The art of poetry in blank verse in 1680, with later editions in 1684 and 1709, as well as original pieces, chiefly An essay on translated verse (1684, 1685). Contemporary critics praised his work at least partly, perhaps, because it was written by a nobleman of somewhat higher moral standing than those around him at court; later scholars note that he was the first commentator to acknowledge the importance of Milton's Paradise lost.
During the exclusion crisis he apparently accompanied James (qv), duke of York, to Scotland during the latter's banishment from court in London. He died in London on 17 January 1685, and was buried in Westminster abbey on 21 January.
Roscommon married first (April 1662) Lady Frances Courtenay, daughter of Richard Boyle (qv), 2nd earl of Cork and 1st earl of Burlington, and widow of Sir Francis Courtenay of Limerick. She died after December 1672; their son died in September 1675. Roscommon married secondly (9 November 1674) Isabella, daughter of Matthew Boynton of Yorkshire. Her only sister Katherine married Richard Talbot (qv), later earl of Tyrconnell. Roscommon had no other children; his widow inherited the greater part of his estates, which subsequently passed into the family of her second husband, Thomas Carter (qv) (d. 1726) of Robertstown, Co. Meath. Roscommon's portrait, painted by Carlo Maratta (or Maratti), is in the collection of Earl Spencer; a watercolour version is in the National Portrait Gallery, London.