In GoodFellas, Martin Scorsese's upcoming organized crime saga, Robert De Niro gives a dazzling performance as Jimmy Conway, a ruthless Irish-American thief and killer. Although De Niro has played everything from boxers and bounty hunters to pyscho taxi drivers and priests over the past 20 years, he truly shines when portraying outlaws like Conway. And no wonder. He's had a lot of practice. In one of his first films, Roger Corman's Bloody Mama (1970), he played a rampaging member of the Depression-era Ma Barker gang. In 1971, De Niro did a turn as a thieving mafioso in the farce The Gang That Couldn't Shoot Straight, based on Jimmy Breslin's best-seller. As the hyperkinetic young hood Johnny Boy in Scorsese's Mean Streets (1973), De Niro racked up impressive reviews and he solidified his reputation soon after when he won a Best Supporting Actor Oscar for his role as the young don in the making in The Godfather, Part II (1974). In the sprawling epic Once Upon A Time in America (1984), he showed up as a Jewish gangster, David ''Noodles'' Aaronson. And in The Untouchables (1987), he demonstrated his home-run swing in a brief appearance as the explosive Chicago crime boss, Al Capone. When it comes to discussing his life in crime, however, De Niro always stays in character. He takes the fifth.