Britain’s Sacha Baron Cohen is about to become famous here in “U.S. and A.,” as Borat calls it, and very wealthy to boot. His movie is a chattering-class sensation, and the rights to his next film sold for $42.5 million before “Borat” even made a penny. His career is on fire, but the man himself is a total enigma. Baron Cohen, 35, rarely gives interviews out of character. He guards his privacy so fiercely that, according to the U.K. press, his publicists denied not only that he attended a party for “Borat”’s recent London premiere, but also that a party even occurred . (It did.) When NEWSWEEK contacted his cousin Simon Baron Cohen, a psychologist and one of the world’s chief experts on autism, Dr. Baron Cohen demurred via e-mail: “I must respect Sacha’s wish for privacy.”

Those who work with him, though, claim that Baron Cohen’s reclusiveness is partly a calculation to keep Borat front and center. “He’s protecting the product,” says Charles. Baron Cohen’s pals describe him as polite, whip-smart and not remotely shy. But his defining characteristic is his total commitment–to nailing every detail, to upping the ante, even to practicing his faith. There are plenty of Jews in comedy, but how many keep strictly kosher and won’t use a phone on the Sabbath? “If it’s an emergency, he’ll answer an e-mail,” says Roach. “But he really does shut down on Friday nights and Saturdays. For ‘Saturday Night Live,’ he obviously broke the rules”–Borat kicked off the Oct. 28 episode–“but it wasn’t without plenty of discussion.”

Baron Cohen didn’t grow up wealthy–his father owned a fine-clothing shop–but the family was cozy enough to live in an upscale London suburb and send the kids to top schools. Sacha, the second of three brothers, attended the Haberdashers’ Aske’s Boys’ School, then Cambridge. In his third year, he visited the United States to research a dissertation on black-Jewish relations during the civil-rights era, and along the way he scored an interview with the reclusive activist Bob Moses. “Moses was revered, deified by some, and he was not talking to anybody,” says Clive Webb, a pal of Baron Cohen’s at Cambridge. “To this day I have no idea how Sacha managed to pull it off.”

Baron Cohen’s parents hoped he’d become an academic, but Sacha had already fallen for comedy. His break came in 1998, when he introduced Ali G on a show called “The 11 O’Clock Hour.” He quickly landed “Da Ali G Show,” which migrated overseas to HBO in 2003. He now lives in L.A. with his Australian fiancée, Isla Fisher, who played Vince Vaughn’s wacko lover in “Wedding Crashers.” “One of our things is to joke excessively, verging on inappropriately, about each other’s wives and girlfriends,” says Roach. “He’s quick to bust someone’s chops, even with people he’s just met. But you feel slightly flattered that he bothered to make fun of you.” Borat’s victims, alas, probably don’t.