DRAMATIS PERSONAE
KING HENRY THE FOURTH – King of England
HENRY, PRINCE OF WALES – eldest son of Henry IV; nicknamed "Hal" or "Harry"
JOHN OF LANCASTER – represented in the play as the King's second son, although he was actually the third
EARL OF WESTMORLAND
King Henry IV of England, (1367-1413). Though his family name was Plantagnet, he was widely referred to as Bolingbroke before taking the throne, after the castle near Spilsby in Lincolnshire where he was born. 
 
 A 16th century portrait of Henry IV, via  Wikimedia Commons. 
 According to Holinshed, his reign was difficult from the start: 
 sith it was euident inough to the world, that he had with wrong vsurped the crown, and not onlie violentlie deposed king Richard, but also cruellie procured his death.   (Cited in the  Arden  edition, p. 136) 
 Though he’s the eponymous King of the play, he speaks only 341 lines, well behind Falstaff, Hal and Hotspur. 
 
 The Arden Shakespeare: King Henry IV , ed. David Scott Kastan (London: Thomson Learning, 2002)
Henry IV Part 1 Characters of the Play