Robert Devereux, 3rd Earl of Essex (11 January 1591 – 14 September 1646) is an English Parliamentarian and soldier during the first half of the seventeenth century.

With the start of the English Civil War in 1642 he becomes the first Captain-General and Chief Commander of the Parliamentarian army, also known as the Roundheads.

However, he is unable and unwilling to score a decisive blow against the Royalist army of King Charles I.

He is eventually overshadowed by the ascendancy of Oliver Cromwell and resigns his commission in 1646.