I've always been fascinated with actors who have to be heroes, whereas I shy away from that," Ricky Gervais, the British comedian who will star in a new HBO series, "Extras," this fall, was saying the other day. "I'm a flawed character. I'm good at that." He uses a Yiddish word for loser. If you want that sort, Mr. Gervais says, then "I'm your man. If you want John Wayne, forget it." Mr. Gervais plays an extra who considers himself a great actor. Oh? And why does he think he brings such verisimilitude to portraying losers? There's a long and...