Lost - Season 6 - Eps 17: The End
For different reasons, Jack and the Man in Black both use Desmond to extinguish the light at the heart of the island. The island starts disintegrating, but The Man in Black is also made mortal. Still desperate to escape, The Man in Black fights Jack and mortally wounds him, but with help from Kate, Jack kills him. Realizing his destiny, Jack sacrifices himself to relight the heart of the island, so his friends can escape on the Ajira plane. Hurley takes Jack's place as protector of the island and makes Ben the new advisor. The flash sideways is revealed to be a type of limbo, or holding pattern, for the main characters, where they reside until accepting their life and death, and are then able to "let go" and "move on" together.
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