The old man in The Road
What if it was Judge Holden who had finally won and killed us all but in his victory he became purposeless and weak and enfeebled and full of despairing regret for all he had done. A being with such depravity and power now a wretch in the wasteland who will never die.
Edit: FYI this theory is neither likely nor verifiable. Just a need idea my brain spawned a few minutes ago.