pinotfan you raise a wonderful issue.
For example, I consider the two greatest writers (fiction) of all time to be, in order, Aeschylus and Shakespeare.
Why? Aeschylus wrote something - the Oresteian Trilogy - that encapsulates maybe all of the most important issues that society has to deal with - loyalty, justice, family, social and political organization, what is owed to the god(s) and to fellow citizens etc. In Prometheus Bound, or the extant parts of it, he dealt among other things with why civilization is worthwhile, and did so without being blind to its failings or drawbacks.
Shakespeare was close to being as broad in what he dealt with, but if Aeschylus, who for us means only a few complete works, is Sandy Koufax, Shakespeare is Walter Johnson - one great work after another, which as a body deal with almost everything.
I am a poor critic or analyst of literary style (I know when I like something but that is about the limit of my abilities there) but I think on writing style both of these authors stand very high as well.
I think just as highly of Aristotle in the field of philosophy or social thought, read the "Politics" I tell my students, even where Aristotle is wrong he is asking all the most important questions - what should be important, what makes a political community, what things are necessary but not sufficient conditions for having one, why is this the most important thing in the world and so on.
In music I would be hard-put to even figure out who is in second place behind Beethoven, I am so convinced he is that far ahead of the field, like Secretariat running the Preakness, but I suppose it would be Bach. But Bach is merely great. Beethoven seems to have incorporated everyone and everything (speaking of Western music only of course) that came before him and then doing more with it than the sum of their parts AND adding something else. When the voices start to sing in the 9th Symphony, no matter how many times I hear it, I come away convinced that the world has changed.
So here, unlike with the examples of authors, the criteria is not "who set the whole thing up for us to discuss ever since?" but rather "who summed the whole thing up and took it miles further?"
Bob Dylan partly fits this last criteria - today it is not just the great songwriting over a period of especially 6-7 years that most amazes me, but that Dylan has an encyclopedic knowledge of American music and all of its various root streams - Gospel, Appalachian music, Delta Blues, Jazz, Country, Western and Cowboy music, and so on. Yet what he did with it made it something else entirely.
So leaving these threads, I will mention an interesting conversation I had years ago with an anarchist girlfriend, once a very well-known figure in the punk movement in first LA and then NY. She said "we all had this idea that the revolutionary thing about punk was that anyone could do it. It wasn't restricted only to people with a certain talent and we were breaking down the musician/fan/spectator hierarchies. But the fact is, the Sex Pistols really were a whole lot better than everyone else."