Bendis!
Marvel's comics were my entrance to the entire comic book world, but Brian Michael Bendis was the writer who eventually made me care about writers. When I realised the effect his cadence had on my reading experience, I began to look at the names of the creators on comic covers instead of focusing solely on the titles. Before that, credits were gibberish. His Ultimate Peter Parker was the first version I'd read with a real appeal to me. The period after I picked up that random issue near the start of Bendis's epic run caused a minor vexation in my best friend, who briefly felt that I was attempting to usurp his fixation on Spidey instead of staying in my own little X-Men realm.
I'm actually quite excited to see a DC book by Bendis now, but it'd be even better if it didn't mean the end of his Marvel work. Exclusivity's an emetic, man.
Bonus Question!
What effect has Brian Bendis had on your life outside of comics?
He provoked an interest in David Mamet, which is why I've seen "Glengarry Glen Ross".