Robert Devereux, 3rd Earl of Essex, KB, PC was an English Parliamentarian and soldier during the first half of the 17th century. With the start of the 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.

The English Civil War refers to a series of civil wars and political machinations between Royalists and Parliamentarians in the Kingdom of England from 1642 to 1651. Part of the wider 1639 to 1653 Wars of the Three Kingdoms, the struggle consisted of the First English Civil War and the Second English Civil War. The Anglo-Scottish War of 1650 to 1652 is sometimes referred to as the Third English Civil War.