He was known to be sick. He collapsed a few days after attending the New York Comic Book Convention (Feb. 23-25) with, they said at the time, "a touch of pneumonia." Other complications were found and he never left the hospital.
During his career, he wrote all the major characters for DC Comics but distinguished himself especially with his co-creations, Deadman, The Doom Patrol and Stanley and His Monster.
Seeing as how I have characters from The Doom Patrol tattooed on my flesh, yeah, this one sucks. True, my love of those characters came during a time Grant Morrison was writing them, but they would never have existed without this incredible man.