John Pym

‘…There were, however, two of the household at Woodstock, who appeared not so entirely reconciled with Louis Kerneguy or his purposes. The one was Bevis, who seemed, from their first unfriendly rencontre, to have kept up a pique against their new guest, which no advances on the part of Charles were able to soften. If the page was by chance left alone with his young mistress, Bevis chose always to be of the party; came close by Alice's chair, and growled audibly when the gallant drew near her. "It is a pity," said the disguised prince, "that your Bevis is not a bull-dog, that we might dub him a roundhead at once— He is too handsome, too noble, too aristocratic, to nourish those inhospitable prejudices against a poor houseless cavalier. I am convinced the spirit of Pym¹  or Hampden.…

1) John Pym (1584-1643), the Parliamentary leader, prominent in the impeachment of Buckingham, Strafford and Laud. He was one of the "five members" whose attempted arrest by Charles I in January. 1, 1642 hastened the outbreak of civil war.’

Puritan John Pym was a leader in the Long Parliament, and was very much in opposition to King Charles I, as the note to the text of Walter Scott’s “Woodstock” above attests.  “Woodstock” was set in 1651, around Charles I’s son Charles II’s escape from England.  Among other accomplishments, John Pym also negotiated the Solemn League and Covenant in 1643, not long before his death, which occurred on December 8^th, 1643. 

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.