Montrose

...' There is but One,' said Allan M'Aulay ; ' and here,' he said, laying his hand upon the shoulder of Anderson, who stood behind Lord Menteith, ' here he stands !'

The general surprise of the meeting was expressed by an impatient murmur; when Anderson, throwing back the cloak in which his face was muffled, and stepping forward, spoke thus :—' I did not long intend to be a silent spectator of this interesting scene, although my hasty friend has obliged me to disclose myself somewhat sooner than was my intention. Whether I deserve the honour reposed in me by this parchment will best appear from what I shall be able to do for the King's service. It is a commission, under the great seal, to James Graham, Earl of Montrose, to command those forces which are to be assembled for the service of his Majesty in this kingdom.'...
 
Walter Scott published "A Legend of Montrose" in 1819.  His named subject, James Graham, 1st Marquis of Montrose, was executed at Mercat Cross in Edinburgh on May 21, 1650.  The Wars of Montrose which transpired between 1639 and 1645 form a backdrop for the novel.
 
As a young man, Montrose became a Covenanter, signing the National Covenant in February 1638.  At least in part what instigated Montrose to join this cause was against the imposition of Laud's prayer book on the Scottish Kirk. 
 
Montrose is best known as a military man, and he gained his first experience leading Covenanter's troops in the First Bishop's War (1639).  After signing the Pacification of Berwick, Montrose ran afoul of Archibald Campbell, who was outwardly supportive of the Covenanters, but Montrose's suspected he had a contrary agenda.  Montrose's opposition to Campbell contributed to an invasion of England under the Second Bishop's War (1640).
 
Montrose corresponded with Charles I after the Bishop's War ended, later opposing the Solemn League and Covenant, which allied Scotland with English Parliamentarians against Charles.  He became a staunch Royalist, which is how Scott portrays him in the novel.