Harry Percy (a.k.a. "Hotspur"), the son of the Earl of Northumberland, is a young nobleman who leads the rebellion against King Henry IV. A courageous and impetuous young leader, he's got a "hot" temper, eats enemy soldiers for breakfast, and has a serious thing for "honour."
The first time we hear about Hotspur, King Henry admires him for his courage on the battlefield at Holmedon, where he's taken several important prisoners captive (1.1). Despite the fact that Hotspur tests the king's power by refusing to give up his prisoners, King Henry gives him serious props – he calls him the "theme of Honor's tongue" and says his behavior is that of a "prince" (1.1.80).
When Henry goes on to say he wishes Hotspur, not Hal, were his son, we see that Hotspur's courageous action is a foil to the prince's wild and dishonorable behavior. This allows the play to explore that traits and qualities that make one a good leader, which is an important thematic issue in the play. Even after Hotspur decides to lead the rebel forces against the king, the play never portrays him as a villain and often makes it difficult to know whether or not he's suited to govern the kingdom. This likely has to do with the fact that Hotspur has a lot in common with King Henry, who also led a (more successful) rebellious uprising in Richard II (the play that precedes Henry IV Part 1 in the tetralogy).
So, how does all of this play out? As Henry IV Part 1 progresses, we see more and more of Hotspur's short-comings. In fact, the very things that seem to make him honorable are the things that render him unfit to lead a country and, ultimately, bring about his downfall. His own father frequently notes "Why, what a wasp-stung and impatient fool / Art thou" (1.3.244-245). Hotspur is rash, impetuous, incapable of strategy, and tends to alienate his colleagues. When Hotspur learns that his father and Glendower won't be joining the rebel forces at Shrewsbury, he forges ahead anyway because he thinks winning an impossible victory will lend "luster and more great opinion" to the rebels' enterprise (4.1.81). Hotspur may be more honest and straightforward than Prince Hal, who schemes and plots his way through the play, but Henry IV Part 1 makes clear that strategy, command of language, and patience are all necessary components of kingship.
Hotspur is the quintessential manly man, who hates all things effeminate. In recent years, literary critics have turned their attention to Hotspur's notions of masculinity, which are linked to his ideas about honor. Honor, we know, is achieved on the battlefield in Henry IV Part 1 and the field of war, Hotspur insists, is no place for effeminacy. So, when a "certain lord" arrives on the battlefield at Holmedon to collect the king's prisoners, Hotspur is livid because the guy is as "fresh as a bridegroom," "perfumèd like a milliner," and talks like a "gentlewoman" (1.3.34, 35, 37, 56).
Hotspur also prefers the erotics of battle to sex with his wife. When Lady Percy demands to know why Hotspur has kicked her out of his bed, he replies that he's got no time "to tilt with lips" and calls for "bloody noses" and "cracked crowns" instead (2.3.97, 98, 98). While the play certainly doesn't go out of its way to correct Hotspur's sexist and obnoxious views, it does seem to recognize the shortsightedness of Hotspur's prejudice.
Hotspur is pretty central to our discussion of "Gender," "Language and Communication," and "Power," so be sure to check out "Quotes" for these themes. You can also read more about Hotspur by going to "Character Roles."