The only son of a wealthy Catholic family, Robert Dormer inherited a large fortune while he was still a minor. He became a ward of Philip Herbert, Earl of Pembroke, whose daughter he married in 1625. After travelling in Europe and as far afield as Turkey and the Middle East, Dormer was created Viscount Ascott and Earl of Carnarvon in 1628. He gained a reputation as a sportsman and extravagant gambler, but also served as a gentleman volunteer in the navy during 1637 and commanded a cavalry regiment in the Bishops' Wars.
When the First Civil War broke out in 1642, Carnarvon defied the wishes of his father-in-law Lord Pembroke and declared for the King. He raised one of the first cavalier regiments of horse and fought at Edgehill in Lord Wilmot's brigade. In February 1643, he served under Prince Rupert at the storming and capture of Cirencester then went with the Marquis of Hertford and Prince Maurice in the cavalry force that joined Sir Ralph Hopton's Cornish army advancing from the west. Carnarvon gained a reputation as a courageous and gallant cavalry officer in the south-western campaign of 1643. He was wounded at the battle of Lansdown, but during the subsequent withdrawal he joined Prince Maurice and Lord Hertford to break out of Devizes and bring reinforcements from Oxford. Carnarvon took part in the battle of Roundway Down, where his advice to Lord Wilmot regarding Sir William Waller's tactics helped to secure the Royalist victory.
After the fall of Bristol, Carnarvon led a force of 2,000 horse and dragoons into Dorset. In early August 1643, Dorchester, Weymouth and Portland surrendered to him on generous terms. When Prince Maurice arrived with the bulk of the Royalist western army, however, the terms Carnarvon had agreed were not honoured and the towns were plundered. Carnarvon resigned his command in protest and joined the King's army at the siege of Gloucester. He remained with the King during the subsequent pursuit of the Earl of Essex's army and was killed at the battle of Newbury on 20 September 1643.
References:
Ian Roy, Robert Dormer, first earl of Carnarvon, Oxford DNB, 2004