The Coldstream Guards is presently a Light Role Infantry battalion of the British Army. It is distinguished by being the oldest unit of the British Army continually in existence, tracing its founding back to August 13, 1650 by Oliver Cromwell as part of the New Model Army. Following his defeat of Royalist forces, Cromwell promoted a Colonel by the name of George Monck to General, and gave him a Regiment formed of smaller units, naming it 'Monck's Company of Foot.' After Cromwell died in 1658, Charles Stuart (Charles II, not Bonnie Prince Charlie), who had been defeated by Cromwell, returned to London to seize power. Monck assembled his Regiment of Foot at a small town called Coldstream, from whence he marched on London, deposed the Army grip on government, and promoted the free elections of the Parliament. When the Parliament was assembled, it voted to restore the monarchy, and Monck traveled to meet the returning King at Dover.
The Government disbanded the New Model Army, and in concession to Monck's service, decreed that his Regiment would be the last disbanded. However, in January 1661 (two days before it was due to be disbanded) a revolt sprung up, and Parliament called on Monck's regiment to quash it, which it did successfully. As a result, the order to disband it was repealed. In February, Monck's Regiment of Foot symbolically laid down their arms as a unit of the New Model Army, and immediately took them up again as Royal troops in the New Standing Army. The Regiment was listed as the second Royal house guards after another unit; in response, the members of the Regiment (which was older than the first so listed) adopted the motto Nulli Secundus (Second to None). They were renamed the Coldstream Guards upon Monck's death in 1670 as the Duke of Albemarle, in recognition of their mustering place as part of the Restoration of the Monarchy, and have remained in service to this day.
Although they are headquartered at Windsor in recognition of their status as a Royal Guards regiment, the Coldstream does not solely perform ceremonial duties. They provide a special unit, known as 'No. 7 Company,' which serves as the Queen's Guard around Windsor Palace and other ceremonial troops, although this unit should not be confused with the Beefeaters, who are typically retired military. No. 7 company is typically staffed by men recently out of training, and both No.7 Company and the First Battalion deploy overseas as part of regular combat units.
The Coldstream Guards make an indirect appearance in Sherlock Holmes, when a commissionaire is identified in The Naval Treaty as having belonged to the regiment. BlackPawn tells me that they are also namechecked in the song Blood Sports for All, by Carter USM.