One night last December, Jason Alexander took a small group of friends, including Wayne Knight, Seinfeld's Newman, to the Magic Castle, an L.A. nightspot specializing in Vegas-style legerdemain. After applauding the club's illusionists, Alexander, a magic buff since childhood, went to a private room and began to prestidigitate in front of his pals. "He did spoon bending like Uri Geller," recalls his friend Ken Solomon, president of Studios USA Television, with whom Alexander, 38, recently signed a deal to produce sitcoms and dramatic series. "He was making coins vanish. He did some card tricks, guessing cards and pulling cards out of fruit. We literally stayed all night."

Alexander, the great magician? To those who know him only from Seinfeld, that's as believable as George Costanza, his insecure and ever scheming alter ego, posing as a marine biologist (to impress a girlfriend), pretending he's gay (to break up with another woman) or faking a handicap (to get his own bathroom and other perks at work).

But for Alexander, a happily married father of two, sleight of hand is but one of many talents he has up his sleeve. "The people who know him only as George don't understand what a wonderful singer-dancer-performer he is," says Robert Iscove, who directed Alexander last year as Lionel, a bumbling palace courtier in ABC's remake of Rodgers & Hammerstein's Cinderella. "If you look at him and that body, you don't expect him to dance and move very well, but he's very good at that, and he has a wonderful Broadway voice."

Indeed, away from Seinfeld, the song-and-dance man in Alexander is always bursting to get out. "We used to both get our shots from the same allergist's office," recalls NBC Entertainment president Warren Littlefield. "When Jason went in, it would become like a musical comedy. He'd start singing out, 'Oh, ladies? And they'd all fight to see who got to give him his shots."

Even as a pudgy, picked-upon kid named Jay Greenspan, growing up in Livingston, N.J., he seemed Broadway bound. "I'm 5 years old, listening to Man of La Mancha and The Fantasticks," he told PEOPLE in 1996. His father, Alexander, an office manager, and mother, Ruth, a nursing-school director, encouraged Jay's showbiz ambitions. After a rocky start (as a Norse explorer in his fourth-grade play he was so nervous he threw up onstage), by age 15 he was poised enough in school plays (The Sound of Music) and community theater to take a stage name: Jason (after his mom's nickname for him, Jay-my-son) Alexander after his dad).

In 1981 he made his Broadway debut in Stephen Sondheim's Merrily We Roll Along. Eight years later he won a Best Actor Tony as the narrator of the musical Jerome Robbins' Broadway. But signing on as Jerry Seinfeld's buddy in 1989 was a breakthrough. "He had done a series of despicable roles in movies like Pretty Woman," says Seinfeld composer Jonathan Wolff, recalling Alexander's turn as a lecherous lawyer who tries to rape Julia Roberts. "He wanted to do a character that wasn't so bad—like George."

"I sort of did a shameless Woody Allen impression for the first few episodes," Alexander told the Bergen, N.J., Record in 1992. "Then I discovered if I just sort of did Larry [David, the show's co-creator, who based George on himself], it would work. That's how he got better defined." Others are convinced Alexander injected a bit of his own DNA into the character. Playing George "wasn't a complete stretch for Jason," Seinfeld coyly told Playboy last year. "Jason always has allergies and ailments that are very Costanza-esque."

In fact, Alexander got so immersed in his character that his costars were sometimes taken aback. Once, for an argument between George and his father, he encouraged a reluctant Jerry Stiller (Frank Costanza) to smack him in the head. "He said, 'It's important,' " recalls Stiller. "He showed me how to do it with the palm of my hand. I bounced it off the little bald area he has. Of course we got a huge reaction. Then Estelle [Harris, who played George's mother, Estelle] said, 'Can I hit him too?' Larry David told her, 'No, only one person can hit Jason at a time.' "

In real life, who would want to? Alexander "is very generous and very caring," says writer Michael Markowitz, who has coscripted a sitcom pilot with him. Indeed, in addition to being a devoted husband (to actress-writer Daena Title, 41) and doting dad (to sons Gabriel, 6, and Noah, 2), Alexander helps pay the medical bills for his older sister, Karen Van Home, 50, a Houston accountant, who suffers from scleroderma, an autoimmune disorder. "As long as I'm alive, I'm going to take care of her," he told PEOPLE.

Meanwhile, wary of being forever typecast as George, Alexander has in recent years tried to distance himself. He took the role of Buzz, the gay, tutu-wearing, butt-baring character in the 1997 film Love! Valour! Compassion! in part, he has said, because it was such a complete departure from the homophobic Costanza.

Still, says Ken Solomon, "I don't think that Jason wanders around going, 'Oh my God, I'm never going to escape this character!' " Besides, adds Cinderella director Iscove: "Once there's a new role, [fans] will latch on to that persona." Making George vanish from memory? That would be Alexander's most impressive trick of all.

This week's cover

On Newsstands Now!

Saved by the Bell Reunion

The hookups, the meltdowns, the memoires

The case reveals what was really going on what they think of each other now!

Get 4 FREE PREVIEW Issues! Click here now