Which actor has done the most to improve the image of science fiction?

There was a time when people thought science fiction (and fantasy) required over-the-top acting and scenery-chewing. Many actors didn't entirely take these roles seriously. That time is past. But which actor, in particular, has done the most to improve the credibility of genre film and television?

Please include a picture or clip showcasing this acting paragon, plus his/her name, and a few words about what they've done to change things, either with their performances or with their attitude towards genre fare.