What role does Captain Beatty play in Montag's development as a character in Fahrenheit 451?
Beatty seems to be the antithesis to Montag. In many ways, he is instrumental in Montag's development. Beatty provides the absolute justification for the Status Quo in terms of why the firemen are needed, their importance, and why they do what they do. He is vital for how Montag sees his consciousness at the outset of the novel. Over time, things end up changing, and Beatty's resistance to this change along with his continual support for the Status Quo help play a role allows Montag to grow in his own right and understand. It is Beatty who ends up forcing the greatest amount of change in Montag as he leads the firemen to burn down Montag's home. This moment of colliding values results in Montag killing Beatty as both values crash into one another. Beatty ends up providing the reference point for assessing Montag's level of change and transformation throughout the novel. Beatty does not change, but Montag does and the more the latter changes it proves to distance himself from the former.
Though Beatty is Montag's enemy I would say that Beatty facilitates Montag's development more than he inhibits it. For example, when Beatty comes to Montag's house to persuade him that books only cause trouble, he seems only to have made Montag even more curious about the world of knowledge and books. Beatty allows Montag a day with a book to make his decision; Montag uses that day to become even further immersed in books. Then, when Beatty burns down Montag's house, he goads Montag by quoting books and using arguments from the books that Montag has come to admire so greatly. Montag is driven by Beatty's words to murdering Beatty, thus committing his first blatant act of crime against society and driving him over the edge to a new life on the run. Thus, Beatty quickens Montag's development from seemingly content member of society to a determined rebel against it.