[2] In an extended flashback, after the death of his wife, Richard Alpert (Nestor Carbonell) arrives on the island as a slave on the Black Rock in the 19th century.

He then encounters the Man in Black (Titus Welliver) and Jacob (Mark Pellegrino), both of whom offer him different deals in exchange for his allegiance.

Prior to her arrival on the island in 2007, Ilana (Zuleikha Robinson) is visited by Jacob in a Russian hospital, where he tells her to protect his remaining candidates (continuing from her flashback in "The Incident").

Following the events of "Dr. Linus", Ilana explains to the survivors that Jack Shephard (Matthew Fox), Sun Kwon (Yunjin Kim) and Hugo "Hurley" Reyes (Jorge Garcia) are candidates to replace Jacob, who was recently murdered by Ben, as protector of the island.

Back to 2007, Richard visits the site where he has buried his wife's necklace, shouting that he has changed his mind and wishes to join the Man in Black.

The episode was written by producer Melinda Hsu Taylor and co-producer Greggory Nations and directed by Tucker Gates.

[4] Emily VanDerWerff of Los Angeles Times gave the episode a perfect score, calling it "awesome" and "another all-timer for the show.

"[5] Maureen Ryan of Chicago Tribune also praised the episode, stating "what was great about "Ab [Aeterno]" is that it showed us a story about one imperfect, well-intentioned man caught up in this terrible struggle.

"[6] Steven Kurutz of The Wall Street Journal deemed it as one of the best hours of TV, "Richard’s story was so dramatic that I found it totally compelling.

"[9] James Poniewozik of Time thought Carbonell "made Richard into another character, showing us the decent, desperate, heartbroken man who would be transformed over 140 years as Jacob's ambassador on the Island.