Already a thread for it, but that's fine.
This is a real bummer. He had so much impact on the industry and most people have no idea about him.
On a lesser note, he was also notable for illustrating that not everyone who sees value in certain elements of Objectivist philosophy was some kind of lunatic; some of it's just common sense.
One of my favorite stories about Ditko involves his work on The Question; his co-writer had sent him a script in which Question said to a criminal some variant of, "Well my friend, you just don't impress me very much." And Ditko sent him a massive letter explaining in crystal clear detail why The Question would never, under any circumstances, refer to any criminal as "my friend", not even in a joking or sarcastic manner.
Things like that are why he had a reputation as being tough to work with, but you have to admire someone who adheres so strongly to their principles, especially about a character they created.
Sad news.