When I was about 13, I realized existence required proof, and the only chance I had of that was to have children (which is unlikely at this point) or to make my mark as an artist. At the time, my interest was in film, so I had hoped I would create a hit film that went on to become a classic. Just one, so my existence would never be in doubt.
Now that I'm in comics, the hope remains somewhat the same. I've been aware for a long time that only a handful of people will attend my funeral, and that the world will not stop moving when I leave it. But I want something left around for people to see and say "hey, that guy did this thing which is kind of impressive."
So to answer this question (which I'm doing now because I have nothing to do at the day job and need a distraction), I want to be remembered for making at least one comic that was a hit, that reached a lot of people, and will be talked about long after I've gone. Because as long as someone somewhere remembers me, I'll never really be dead.