I have finished a fantasy novel I have been writing for the past few years and I am now in the process of meeting with representatives from publishing companies toward the goal of publishing my book.

I do not yet have a satisfactory cover but I am working with an artist now on one and the drafts are coming out magnificent. However, I am not sure if I am wasting my time since I've heard that the publisher can dictate the cover that they prefer.

More generally, must one (or is it at least strongly advised) to submit a manuscript with a cover already designed or does it not matter? Also, does an author have any say over what their cover looks like?