Javier Grillo-Marxuach, a supervising producer and writer on Lost, is leaving the show. He was hired on about two years ago when Lost was just a gleam in J.J. Abrams' eye. On his website, Javi says his gig on Lost was only meant to be a couple of months so he could help create long-term story arcs and basically plan out the series (and write a pilot!). Two years, seven episodes, and "one hanging hobbit" later, Javi said it's the right time for him to leave and let the other writers take the show where it needs to go.

Javi has been one of the most high-profile writers of the show, frequently producing the Radio Free Javi podcasts about Lost and his other interests, including comic books. He also is a frequent contributor to The Fuselage, the ABC-sanctioned forum about the show.

His bio on IMDB says he wrote or co-wrote the following episodes:

House of the Rising Sun (aired Oct. 2004)
All the Best Cowboys have Daddy Issues (Dec. 2004)
Hearts and Minds (Jan. 2005)
...in Translation (Feb. 2005)
Born to Run (May 2005)
Orientation (Oct. 2005)
Collision (Nov. 2005)

Those are all TERRIFIC episodes so, in my humble opinion, there are some big shoes to fill now that Javi is leaving the island. And don't worry about Javi. He'll be fine. He has done a ton of writing for television serial dramas, he has an idea for his own show and is also working on a new line of comic books.