Members of the Knights of the Blackdowns generally impersonate real-life historical characters. Below is a very quick summary of who those people were, in alphabetical order, and I’ll be adding links to more detailed information in due course.
Anthony Woodville, 2nd Earl Rivers, the persona assigned to Cal. The real-life earl’s prominence at court was thanks to Edward IV marrying his sister Elizabeth. He was a famous tournament champion. The title Rivers derived from the family name of the former Earls of Devon (distinct from Devonshire). There’s more information about him here.
Edward, 4th Duke of York. The future King Edward IV of England, played by Tony Mason. Edward’s father Richard pursued the crown until he was killed at the Battle of Wakefield (1460), after which the 18 year-old Edward took up the family cause to defeat the incompetent king Henry VI on his own behalf.
Lady Eleanor Talbot (appears as herself). After Edward IV died, Eleanor claimed she had a pre-contract of marriage with him, preceding his marriage to Elizabeth Woodville, and thus invalidating it. The claim was, however, made on behalf of Richard III who wanted to undermine the legitimacy of Edward’s numerous successors (those who he didn’t have murdered in the Tower of London).
Elizabeth Wayte (appears as herself). Perkyn’s girlfriend’s character was a “naive girl” seduced by Edward and possibly the mother of his illegitimate son, Arthur Plantagenet, 1st Viscount Lisle, among others.
Elizabeth Woodville, the character assigned to Amber, “The White Queen” in popular fiction, married Edward IV secretly in 1464. Their covert and unequal union mirrored her father’s upwardly-mobile pairing 27 years beforehand, to Jacquetta of Luxembourg.
George Neville, Bishop of Exeter, played by Zack, was instrumental in orchestrating Edward IV’s “popular election” to the throne by a crowd at St George’s Fields in London, shortly before the Battle of Towton, in which the forces supporting Henry VI were finally defeated.
George Ripley (appears as himself). The Augustinian canon of Bridlington was one of the most influential alchemical authorities of his time.
Henry Beaufort, 3rd Duke of Somerset. “Henry B” in the book commanded and won the Battle of Wakefield for the Lancastrians, at which Edward’s father Richard was killed, but later transferred his allegiance to Edward, who showered him with attention, and gave him the honour of sharing the king’s bed (a non-sexual mark of favour).
Henry Percy, 3rd Earl of Northumberland, played by the pre-deceased Colin, was the senior Lancastrian to be killed at the Battle of Towton (1461), supporting the cause of King Henry VI. The Percy’s long-standing feud with the Neville family helped to precipitate the Wars of the Roses.
Jane Shore (appears as herself), using the name by which she is best remembered through history. She was one of Edward IV’s most celebrated mistresses, known to have been disliked by Edward’s wife Elizabeth Woodville. In later years Jane was respectably married, and survived into her 80s.
John de Mowbray, 4th Duke of Norfolk, played by Amber’s brother Jon, held the royal office of Earl Marshal by heredity, and was brother-in-law to Eleanor Talbot, through her sister Elizabeth.
John Scoggins, played by Simon Coggins. There’s no special reason to believe the trickster really existed. The chronicles of this character’s exploits in the company of the kings of England and France were probably only made a century later.
John Tiptoft, 1st Earl of Worcester, played by John Butcher, was Lord High Constable of England, and notorious for his zealous prosecution of the defeated Lancastrians, and cruel punishments including beheading, quartering, and impalement.
Warwick the Kingmaker aka Richard Neville, 16th Earl of Warwick (appears as himself) was the wealthiest and most powerful English peer of his time. He helped to raise Edward IV to the throne, but they fell out over Elizabeth Woodville’s marriage to the king, which cut across Warwick’s own plans for Edward.