Lost - Season 6 - Eps 15: Across the Sea
Jacob and the Man in Black are revealed to be twin brothers. They are raised by a mysterious woman who is charged with protecting the island. As revenge for the murder of their adoptive mother (who killed their real mother), Jacob throws his brother into the source of electromagnetism after being made the island's guardian, which transforms the Man in Black into the smoke monster.
About Lost

Title: Lost
First Air Date: 2004-09-22
Last Air Date: 2010-05-23
Status: Ended
Rating: 7.945/10 (from 4578 votes)
Language: EN
Seasons: 7
Total Episodes: 118
Network: ABC
Genres: Mystery, Action & Adventure, Drama
Production Companies: ABC Studios, Bad Robot, Touchstone Television
Synopsis
Stripped of everything, the survivors of a horrific plane crash must work together to stay alive. But the island holds many secrets.
Cast

Matthew Fox
Jack Shephard

Evangeline Lilly
Kate Austen

Terry O'Quinn
John Locke

Josh Holloway
James Sawyer

Michael Emerson
Benjamin Linus

Jorge Garcia
Hurley Reyes

Naveen Andrews
Sayid Jarrah

Jeff Fahey
Frank Lapidus

Nestor Carbonell
Richard Alpert

Henry Ian Cusick
Desmond Hume