The conductor of the magically powered Knight Bus, Stan is the cocker-nee, cock-sure lad who must help Harry get from Little Whinging to The Leaky Cauldron, where he has to face the Minister Of Magic about casting a spell in front of muggles.
He’s also a useful source of info – his paper includes plenty of exposition about Sirius Black’s escape from Azkaban in the third film.
Also on the bus? Driver Ernie Prang, who gets one or two lines in the book (“Arr”) and zero in the film. Oh, and a severed head voiced by Lenny Henry.