When Amsterdam-born Ronaldus Shamask opened his business on Madison Avenue two years ago, he ducked into the back room whenever the buzzer rang. His partner, Murray Moss, took on the customers. "I was too personally involved in the clothes to deal with clients," recalls Shamask, 35, whose bold geometric designs are strongly influenced by traditional Japanese attire. "I approached what I was doing as art. Then I realized nobody wants to buy art to wear so it is better not to discuss it."

Back in 1979 hardly anyone was talking about Shamask. In the austere new quarters they called their laboratory, Shamask and Moss opted for Zen-like simplicity—no name next to the downstairs buzzer, one Art Deco vase in the front hallway, and white linen Japanese screens in the second-floor windows. "We were very naive," Moss, 32, says. "We felt it was poor taste to display clothes."

But their idiosyncratic approach to the rag trade worked. In New York, Bergdorf Goodman is now putting the finishing touches on a Shamask boutique; it will open early next month. His line of fall and winter coats, jackets and dresses will soon be en route to more than 20 stores across the country, including Sakowitz in Texas and I. Magnin in California. "I haven't seen workmanship like his in a very long time," raves Saks fashion director Ellin Saltzman.

And the celebrity trade—fashion's equivalent of a papal blessing—has started flocking to his door. Shamask's strong architectural shapes quickly caught the eye of Valerie Harper and Shelley Duvall. Polly Bergen bought this season's envelope coat in black wool for $900. A few weeks ago Donald Sutherland strolled in with companion of nine years Francine Racette and paid $450 for an angular "Shamoishei" jacket in white textured cotton. Earlier this summer Bianca Jagger went off with Shamask's plaid silk taffeta jump suit ($650).

The designer's independent streak has been with him ever since he was growing up in a seedy section of Amsterdam. Though he ran with a street gang, he also helped his mother care for three younger siblings, picking them up at school, feeding them and putting them to bed. "Living in Holland was the most frustrating and stifling experience," Shamask says now. "I was taught nothing is possible. Maybe that was the reason for my rebellion."

After leaving school at 15, he moved with his family to Melbourne, Australia. There his father, an unemployed ship welder, looked for work and Ronaldus struck out on his own doing window displays for a large department store. Seven years later he left for London, where he worked as a fashion illustrator and commercial artist.

Shamask came to the U.S. in 1969 to do posters, costumes and stage sets for a theater company in Buffalo. By the mid-1970s he had settled in Manhattan, where he started making coats and clothes for a few private clients. At his first public showing in 1979, cellist Frederick Zlotkin played Bach while models in black and white linen walked down the runway at an agonizingly slow pace. Since then Shamask's fascination with the Orient has been clearly reflected in his unadorned designs. "I don't do beads and ruffles," he says. "With my clothes, every seam has to have a purpose."

Shamask lives with interior architect Eva Ching, 32, on Manhattan's Upper East Side and likes to unwind watching Japanese films. His sense of perfection is only now beginning to admit a few concessions. "I know that not everyone is a size 8," he confesses, "and that life in America is not the same as life in 10th-century Japan."