4. Mark Whitacre - The Informant!
Damon re-teamed with his frequent collaborator Steven Soderbergh for 2009's The Imformant! Though not one of Damon's biggest hits, it does feature one of his most nuanced and committed performances, playing corporate whistle-blower Mark Whitacre. Based on a true story, the role required Damon to gain between 20 and 30 pounds to more closely resemble the doughy protagonist, though this is not merely a gimmicky turn for the actor; Damon has such a strong grasp on the tone Soderbergh is shooting for that he couldn't fail. The film was divisive because of its oddly comic, idiosyncratic tone, but Damon perfectly interprets it, delivering a performance that represents Whitacre as a hilariously downtrodden, desperate sad sack thrown into an impossible situation and simply clawing to get out. Though Damon was nominated for a Golden Globe, he certainly should have had more attention on the awards circuit that year.