Dramatis Personae
KING EDWARD IV
EDWARD, PRINCE OF WALES
afterwards KING EDWARD V, King's son
RICHARD, DUKE OF YORK, King's son
Edward Plantagenet had seized the throne from King Henry VI (a Lancastrian), whose reign and deposition had been portrayed in Shakespeare’s  Henry VI  plays. 
 He narrowed his base of support by offending the powerful Earl of Warwick with a secret marriage to Elizabeth Woodville ( depicted in  3 Henry VI , then defeated Warwick’s forces ( depicted later in the same play. ) 
 
 King Edward IV, via  Wikimedia Commons.
King Richard III Characters of the Play