Sir John Falstaff is a fictional character who appears in three plays by William Shakespeare and is eulogised in a fourth. His significance as a fully developed character is primarily formed in the plays Henry IV, Part 1 and Part 2, where he is a companion to Prince Hal, the future King Henry V of England. Falstaff is also featured as the buffoonish suitor of two married women in The Merry Wives of Windsor. Though primarily a comic figure, Falstaff embodies a depth common to Shakespeare's major characters. A fat, vain, and boastful knight, he spends most of his time drinking at the Boar's Head Inn with petty criminals, living on stolen or borrowed money. Falstaff leads the apparently wayward Prince Hal into trouble, and is ultimately repudiated after Hal becomes king.

Falstaff has since appeared in other media, including operas by Giuseppe Verdi, Ralph Vaughan Williams, and Otto Nicolai, and in Orson Welles' 1966 film Chimes at Midnight. The operas focus on his role in The Merry Wives of Windsor, while the film adapts from the Henriad and The Merry Wives. Welles, who played Falstaff in his film, considered the character to be "Shakespeare's greatest creation".