I wouldn't say it was one person. Druckmann, and the director for the first game, Bruce Straley, pitched it together after they re-worked Druckmann's original pitch to George Romero. Romero tasked university students with pitching him a game concept. Druckmann's idea was to blend "Ico" the ps2 game, with Night of the Living Dead, with John Hartigan from Sin City. His idea didn't win, by the way.
The co-presidents of ND liked the idea, though, and they tasked Druckmann and Straley to work together. Druckmann's initial plan was for the Human Cordyceps strain to only infect women, too, with the policeman having a heart condition and the little girl needing to protect him every so often. This eventually evolved into The Last of Us, with central themes around the idea of "life goes on."
Oh, Bruce Straley left the company after Uncharted 4 dropped, He directed Uncharted 2, 4 and TLOU 1.
Edit: He left after uncharted 4, not tlou 1, whoops. I got the release dates of both games switched around, sorry.