It is doubtful that the model for Falstaff was an actual highwayman, but it is possible he was not as well behaved as would have been expected by his family, perhaps a black sheep.
Falstaff appears in several of Shakespeare's plays, but there is contention whether he is the same in all. Goddard finds a rather schizophrenic portrait of both Falstaff and Henry IV.
A colossus of sack, sensuality, and sweat -- or a wit and humorist so great that he can be compared only with his creator, a figure, to use one of Shakespeare's own great phrases, livelier than life? One might think there were two Falstaffs he truth is that there are two Falstaffs, just as there are two Henrys, the Immortal Falstaff and the Immoral Falstaff, and the dissension about the man comes from a failure to recognize that fact. That the two could inhabit one body would not be believed if Shakespeare had not proved that they could. That may be one reason why he made it so huge."
The first character who comes to mind when I think of Falstaff is Lex Luthor in the Smallville and Superman series. He was a good friend to the youthful Superman, in spite of being somewhat self-centered and a bit of a rogue. He was even sometimes funny, though not the comic relief of Falstaff. One might think that Lex Luthor represents the two sides of Falstaff, the friendly rogue in Smallville and the more serious viallain, that is an outlaw, in Superman. There are really quite a few parallels in modern literature, especially if you include movies as literature. It seems that Shakespeare's idea to provide comic relief has been widely imitated.
Bloom sees Falstaff as the penultimate comic wit, and credits him as one of Shakespeare's greatest creations.
Falstaff is of the company both of the heroic wits, Rosalind and Hamlet, and of the heroic vitalists, the Wife of Bath and the Panurge of Falstaffian Rabelais. He could also ride into the world of Sancho Panza and the Don, because in some sense he is their synthesis, fusing Sancho's ribald realism and the Don's faith in his own imagination and in the order of play. The Don's chivalric madness is shared by Hotspur, and not at all by Falstaff, but Cervantes is perhaps the only author except Chaucer, and Shakespeare himself, who could have imagined Sir John Falstaff. Hazlitt charmingly remarked that the Fat Knight "is perhaps the most substantial comic character that ever was invented," and certainly Falstaff is the patron of all fat men forever.
Bloom 2) have to agree with Bloom, as I found this character to be the most engaging of all those in this play. I do not wonder that Elizabethan audiences loved him, as he seems to bridge the gap between nobility and the common man, between educated and illiterates, yet he remains more true as a person than most of his betters. He is rogue, but an honest rogue.
It was necessary for Falstaff to be in this play, as Shakespeare could not attribute all the wisdom which Henry IV eventually acquires to internal development of character. The main character actually needed a foil and a sounding board. In addition, the role playing provided a means to communicate ideas and plans which needed some form of conversation to be shown in the play. It also gave some justification to the maturity of Harry's judgment of the nobility, many of whom secretly opposed him. In this play, Falstaff was actually the only character with whom Harry spoke candidly and often truthfully.
Bloom, Harold, ed. Falstaff / . New York: Chelsea House, 1992. Questia. 7 Dec. 2006 http://www.questia.com/PM.qst?a=o&d=102555976.
Goddard, Harold C. "Henry IV." Falstaff / . Ed. Harold Bloom. New York: Chelsea House, 1992. 110-124. Questia. 7 Dec. 2006 http://www.questia.com/PM.qst?a=o&d=102556084.
Weis, Rene, ed. Henry IV, Part 2. New York: Oxford University, 1998. Questia. 7 Dec. 2006 http://www.questia.com/PM.qst?a=o&d=58756856.
Wilson, J. Dover. The Fortunes of Falstaff. Cambridge, England: Cambridge University Press, 1944. Questia. 7 Dec. 2006 http://www.questia.com/PM.qst?a=o&d=270539.