Shakespeare's main source for a number of his history plays, including Henry IV, Part I was Ralph Holinshed's Chronicles of England, the second edition (1587) of which he utilised, mainly as a reference book. Holinshed's book is not followed religiously; on many occasions Shakespeare seems to have manipulated and ignored 'history' so that his plays may be more effective in a dramatic sense. Nonetheless there are many similarities - just as the author of the Chronicles did, Shakespeare confuses the two Edmond Mortimers (a nephew and uncle) and makes them the same character. The 'plot' for his play also seems to be readily present in Shakespeare's main source. Both kings follow policy, they do not shy away from the threat of rebellion, they are unhappy and disappointed in their son's lack of interest in political events. However, Shakespeare develops the character and the psyche of the errant son to a much greater extent, just as Hotspur is developed from a few descriptions of his military prowess and courage, rather than a detailed analysis of his personality. Shakespeare also adds his own, individual dramatic touches to the play - characters such as Falstaff and Lady Percy who provides the emotional centre for the story are almost entirely of Shakespeare's own making.
Samuel Daniel's narrative poem of 1595 The First Fowre Bookes of the Civile Wars Between the Two Houses of Lancaster and Yorke was also a source for Shakespeare's play. This poem follows the historical events of this period and Shakespeare followed the poet when he decided that Glendower would be absent from Shrewsbury (the Welsh were in Holinshed). Shakespeare also developed on the idea that a parallel could be drawn between Hal and Hotspur as military creatures. Daniel's too confused the two Edmund Mortimers.
It was well known that Henry V (Hal) had a wild and debauched youth, Holinshed mentions this and it was also passed on simply by word of mouth. The main literary source for his revelries, however, is likely to have been the anonymous play The Famous Victories of Henry V which was first performed as early as 1586. This play is significantly less sophisticated that Shakespeare's. The language and humour is crude and unsubtle and does not work from the premise of pun, word play and double meaning as Shakespeare's does. Nonetheless there is a character called John Oldcastle (who is Falstaff) and another called Ned who it is thought could be partly Poins. A highway robbery and a play-acting scene do occur in the play as well.