Sir Thomas Lucas (1598 – before October 1649), was a professional soldier from Lexden, just outside Colchester in Essex, England, who served with the Dutch States Army in the Eighty Years War and later fought in the Irish Confederate Wars. The eldest son of a prominent Essex family, Lucas took up a military career after being excluded from inheriting the family estates due to his illegitimacy. He took part in the 1639 to 1640 Bishops' Wars and was subsequently made General of Horse in Ireland. After the Irish Rebellion broke out in October 1641, James Butler, 1st Duke of Ormond, appointed him to the Privy Council of Ireland. Both his brothers served with the Royalist army during the First English Civil War but Lucas remained in Ireland and helped negotiate the September 1643 Ceasefire or "Cessation" with the Irish Catholic Confederacy, which allowed Protestant Irish troops to be transferred to England. Shortly after Charles I surrendered in June 1646, he returned to England and retired to his estates in Lexden after paying a fine. He took no part in the 1648 Second English Civil War, even though his younger brother Charles Lucas (1613–1648) led the Royalist defence of Colchester and was executed after it surrendered. He died sometime before October 1649. Personal details Thomas Lucas was born in 1598, eldest son of Sir Thomas Lucas (1573–1625) and his then mistress and future wife Elizabeth Leighton (died 1647). Shortly before the birth, Sir Thomas fled abroad after killing a member of the Cecil family in a duel. He remained in exile until pardoned by James VI and I and the marriage did not take place until August 1604, making Thomas technically illegitimate. This meant his younger brother Sir John (1606–1671) inherited the family estates, although in 1612 his father purchased him a manor near Lexden, outside Colchester. In addition to John, Lucas had another brother, Charles Lucas (1613–1648) and five sisters, including Mary (1608–1646), wife of Sir Peter Killigrew (1593–1668), Anne (1614–?), Elizabeth (1612–1691), who married Sir William Walter (1604–1675), and Catherine (1605–1702), wife of Sir Edmund Pye (1607–1673). The youngest was Margaret (1623–1673), a prolific author and scientist who in 1645 married William Cavendish, 1st Duke of Newcastle (1593–1676), formerly Royalist commander in Northern England during the First English Civil War. In January 1629, Thomas married Mary Byron (1612–1650) and they had five children together before his death in October