Season 6: “Ab Aeterno” (9.3)
Ever since his introduction in season 3, Richard Alpert had always been one of the most intriguing characters of Lost. “Ab Aeterno” finally peeled back the layers of mystery surrounding his character.
What made the episode such a triumph is that it not only provided answers about Richard, Jacob, the Man in Black, and the Island, but it was also a deeply moving episode on its own and in the larger context of the series. Nestor Carbonell got to shine in a way he never had before in one of the best performances in the entire series.