Robert Devereux, 3rd Earl of Essex KB PC (11 January 1591 – 14 September 1646) was an English Parliamentarian and soldier during the first half of the seventeenth century. With the start of the English Civil War in 1642 he became the first Captain-General and Chief Commander of the Parliamentarian army, also known as the Roundheads. However, he was unable and unwilling to score a decisive blow against the Royalist army of King Charles I. He was eventually overshadowed by the ascendancy of Oliver Cromwell and Thomas Fairfax and resigned his commission in 1646.