Falstaff and Hotspur are two of the most memorable characters in the play, both larger than life. Both are knights, though Hotspur is brave and zealous, taking his vocation very seriously, while Falstaff cares nothing for the conventions of knighthood, being a coward and a glutton. The difference between them is underscored by Hotspur’s speaking in ceremonious blank verse, while Falstaff speaks in colorful prose.
The two knights represent extremes in every sense and are similar principally in being equally extreme in opposite directions. One of the most telling differences between them is shown in their attitudes to honor. To Hotspur, it is a sacred word. In his view, a knight ought to be prepared to go to any lengths to preserve or redeem his honor:
By heaven, methinks it were an easy leap,
To pluck bright honor from the pale-faced moon,
Or dive into the bottom of the deep,
Where fathom-line could never touch the ground,
And pluck up drowned honor by the locks;
So he that doth redeem her thence might wear
Without corrival, all her dignities...
Falstaff has a more practical and less idealist approach. He mocks the ideas of chivalry and honor, asking scornfully.
Honor hath no skill in surgery, then? No. What is honor? A word. What is in that word honor? What is that honor? Air. A trim reckoning! Who hath it? He that died o' Wednesday. Doth he feel it? No. Doth he hear it? No. 'Tis insensible, then. Yea, to the dead. But will it not live with the living? No. Why? Detraction will not suffer it. Therefore, I'll none of it. Honor is a mere scutcheon: and so ends my catechism.
These opposing attitudes to the essence of knighthood illustrate the yawning gulf between Hotspur and Falstaff in their attitudes to every aspect of life. The young Prince Henry, initially the boon companion of Falstaff in his drunken adventures, must steer a middle course between these extremes.
Falstaff and Hotspur are foils to each other: they represent two different kinds of excesses that Henry IV must avoid if he is to become a successful monarch.
Falstaff is a likable character, the ultimate "party guy" who seems to live to have a good time. He is cheerful, even when people make fun of him. However, for all his friendliness, he lacks moral fiber. He is a liar and a robber, as well as a coward who will run away from danger rather than risk himself. He lacks self control and so falls into debt. Further, Falstaff wriggles away from his promise to marry Mistress Quickly. Although he begins as Henry's companion, Henry comes to see that he lacks gravitas. Cheerful as Falstaff is, Henry must distance himself from him.
On the opposite side of the spectrum, Hotspur is too concerned with honor, and as his name indicates, too hotheaded. He has moral fiber and a great deal of courage, but he also is impatient and too willing to judge people hastily and treat them cruelly. For example, he mocks what he thinks are effeminate courtiers and takes a black/white approach to people in general: either you are like him and on his side or unlike him and an outcast. He is also too willing to jump to conclusions without getting all the evidence.
In sum, Falstaff is too laid back and Hotspur too uptight and hotheaded. Because of his lack of character, Falstaff makes bad decisions; because he is too rigid and narrow minded, Hotspur also makes poor decisions. Neither have the leadership abilities Henry needs to rule effectively.
To some extent, Falstaff and Hotspur represent the twin dangers that Prince Hal must avoid if he is to become a wise, benevolent king. One of the most colorful characters in the whole of Shakespeare, Falstaff is an aging delinquent, a lover of wine, women, and song. Not only that, but he's mired in debt, throughly dishonest, greedy, and completely untrustworthy.
By comparison, Hotspur is almost a paragon of virtue. Though something of a firm, unbending moralist, Hotspur shares Falstaff's capacity for bluntness in his language and his interactions with others. Yet crucially he lacks Falstaff's good humor and bonhomie, which makes it difficult for him to impose himself on those around him. Unlike Falstaff, Hotspur takes life—and himself—very seriously indeed. He's fiercely ambitious and has no hesitation in joining his family's rebellion against Prince Hal. Hotspur is so single-minded in his pursuit of glory that he makes the fatal mistake of engaging with the future king of England in mortal combat. One certainly can't imagine Falstaff doing any such thing.
Either way, Prince Hal has been provided with an object lesson in the kind of qualities needed for a king. Once he accedes to the throne, King Henry V, as he'll then be, will combine Hotspur's raw courage and heroism with Falstaff's charisma and people skills to create a paradigm of kingship that will set the standard for centuries to come.
Fallstaff and Hotspur seem like almost complete opposites at first glance. Falstaff plays the role of the "dishonest" fat knight who entertains and is used as comic relief and distraction. Hotspur, on the other hand, is a dramatic character who propels the plot with his actions. However, upon closer look they have some similarities. Hotspur and Falstaff are both described as too big. Hotpsur in spirit, and Falstaff in girth. Similarly, both Hotspur and Falstaff are obsessed with honor and determination, only Falstaff is geared towards making fun of those qualities, and Hotspur is trying to achieve them. There are many similarities and differences between these two fabulous and well rounded characters.