Most students of publishing would answer say, 'the publisher.'
Ask an author, especially one desperately seeking publication, and they would say, 'the editor.'
Ask the editor, enlightened ones would suggest, 'the author,'; others might point to the sales team and cite 'the marketing director' who pushes sales so that books make a profit.
Everyone of these roles is important - a good author creates a successful story; a good editor is needed to represent the reader and catch sticky plot details, along with a good copy editor who catches mistakes the author hadn't noticed. Marketing is increasingly pivotal in putting the book before the reading public. The publisher is a little like a film or theatre producer - no one knows exactly what they do other than take responsibility for finances and pull the team in a forward direction.
But who really are the most important people in publishing?
The answer is quite simple - the reader!
The reader who buys our books, cares about our characters, enthuses over our plots, tells their friends what they liked, champions our books in review pages and, generally, keeps the industry buoyant!
Without you there would be no publishing. Thank you!