Ian Somerhalder, who has the role of Boone Caryle in Lost Season 1, will be returning to Season Six.
Boone Caryle had a relatively major role in the first Season of Lost, until he was killed off near the end of the Season when the Nigerean Beachcraft fell off the cliff with him inside.
It is possible that if John Locke had not lied to Jack and had told the truth about what had happened to Boone, then Jack may have been able to save him.
Also if Jack had gone through with cutting off the 'dead' leg, Boone may have survived.
Somerhalder also made an appearance in Season 3, however it was only in one episode when Locke had a dream in the episode: 'Further Instructions'.
Boone does also appear in another episode of Season Three, however it was just in a flashback from Niki and Paulo's perspective.
Somerhalder offered no other details, but this begs the question of exactly which other season-one characters will be returning to the island for Season Six.
There is no indication as to whether Boone's sister Shannon will be playing a major role in Lost Season Six or if she will be making an appearance at all; She has been offered the role however she has recently appeared in several films and may not have to time to star in Lost Season Six.
However, I think it will be hard for Boone to make an appearance without Shannon, since they are usually played together.