LOCKE
Terry O'Quinn had the greatest range of situations in which to perform. He did quite well. Received Emmy Award nominations in 2005, 2007, and 2010 in the category of Outstanding Supporting Actor in a Drama Series for his portrayal of John Locke. He won the 2007 award beating out, among other nominees, fellow Lost actor Michael Emerson.
BEN
Michael Emerson came to the series as a guest star, but his performance captured the imagination of the fans and producers to where he became a main character. He won an Emmy for Outstanding Supporting Actor In A Drama Series in 2009 for his role as Ben.
DESMOND
Henry Ian Cusick was another guest star who made an impact to become a regular cast member. Cusick, after three guest starring episodes during Season 2, became a series regular at the beginning of the third season. Cusick was nominated for Outstanding Guest Actor In A Drama Series at the 2006 Emmys for his performance as Desmond in the episode "Live Together, Die Alone, Part 1".
ELOISE
Fionnula Flanagan was an accomplished actress prior to a guest role in the series. However, her portrayal of Eloise Hawking made her a mysterious center piece to future story lines bridging the island, Dharma and the Others. As Ben was seen as evil incarnate, Eloise was a much more sinister and powerful force behind the scenes. When she was in a scene, you could see the mental gears churning some devious plot.
One can now realize that these four characters were pivotal in the final two seasons of LOST. O'Quinn's character was reborn in the form of Flocke. Ben's power struggle with Jacob and Widmore led to the chaotic final chase to find a final island guardian. Eloise was all knowing in both worlds, and tried to keep them worlds separated so she would not lose her son, Daniel. And Desmond became the bridge between the island and the sideways realms. In some ways, these four actors pushed themselves in the prime, leading roles as the series wound down.
