I looked at the other thread, but I can't describe him in one sentence. This paragraph comes from the book "Pleasure" by Eric Jerome Dickey, and when I read it, I thought it fit him to a T.

"Suicidal dick. You know, the type of dick that makes you sacrifice yourself, makes you give up all your hopes and dreams, dick that makes you quit your hobbies because you wanna spend 24/7 making his world better. That's what I call suicidal dick."