The Commander-in-Chief of the Forces, later Commander-in-Chief, British Army, or just the Commander-in-Chief (C-in-C), was (intermittently) the professional head of the English Army from 1660 to 1707 and of the British Army from 1707 until 1904. In 1904 the office was replaced with the creation of the Army Council and the appointment of Chief of the General Staff.

Thomas Fairfax, 3rd Lord Fairfax of Cameron, also known as Sir Thomas Fairfax, was an English politician, general and Parliamentary commander-in-chief during the English Civil War. An adept and talented commander, Fairfax led Parliament to many victories, including the crucial Battle of Naseby, effectively becoming military ruler of England, but he was eventually overshadowed by his subordinate Oliver Cromwell, who was more politically adept and radical in action against Charles I. Fairfax became dissatisfied with Cromwell's policy and publicly refused to take part in Charles's show trial. Eventually he resigned, leaving Cromwell to control the country. Because of this, as well as his honourable battlefield conduct and active role in the Restoration of the monarchy after Cromwell's death, he was exempted from the retribution that was exacted on many other leaders of the revolution.