Prince Rupert of the Rhine

Samuel Pepys' diary entry for September 6, 1664 includes references to Prince Rupert, Cromwell,  and Cavaliers.  Prince Rupert was the leading military commander for the Royalists in the English Civil Wars.  Rupert was the grandson of James I of England, through James' daughter Elizabeth.  Rupert learned about the use of cavalry in war while imprisoned, having been captured by forces of the Holy Roman Emperor, while fighting with Dutch forces.  After his release (1642), he went to England, fighting for Charles I.  His efforts were notably felt at the Battle of Naseby, where Rupert led an attack against Parliamentarian forces.  Charles and Rupert's troops were less disciplined than Cromwell's and Naseby ended in defeat the Royalists.

Pepys:

SEPTEMBER 1664

6th. ... This day Mr. Coventry did tell us how the Duke did receive the Dutch Embassador the other day; by telling him that, whereas they think us in jest, he believes that the Prince (Rupert) which goes in this fleete to Guinny will soon tell them that we are in earnest, and that he himself will do the like here, in the head of the fleete here at home, and that for the meschants, which he told the Duke there were in England, which did hope to do themselves good by the King's being at warr, says he, the English have ever united all this private difference to attend foraigne, and that Cromwell, notwithstanding the meschants in his time, which were the Cavaliers, did never find them interrupt him in his foraigne businesses, and that he did not doubt but to live to see the Dutch as fearfull of provoking the English, under the government of a King, as he remembers them to have
been under that of a Coquin. I writ all this story to my Lord Sandwich tonight into the Downes, it being very good and true, word for word from Mr. Coventry to-day.

Prince Rupert is included in Walter Scott's "Peveril of the Peak":

Upon these visits, it was with great pleasure he received the intelligence, that Lady Peveril had shown much kindness to Mrs. Bridgenorth, and had actually given her and her family shelter in Martindale Castle, when Moultrassie Hall was threatened with pillage by a body of Prince Rupert's ill-disciplined Cavaliers. This acquaintance had been matured by frequent walks together, which the vicinity of their places of residence suffered the Lady Peveril to have with Mrs. Bridgenorth, who deemed herself much honoured in being thus admitted into the society of so distinguished a lady.