Having The New York Times call you "the most exciting and original" modern dance choreographer at work today sets the bar high for any artist. But Wim Vandekeybus has met that standard for the past two decades, continually working and evolving with his dance troupe Ultima Vez. Always controversial, his risky creations have garnered both ecstatic raves and complaints of disappointment. What cannot be debated is the firm grasp Vandekeybus and his dancers have on innovation.

They're celebrating their 20-year anniversary with Spiegel ("mirror" in Flemish), a retrospective of the troupe's work that debuted in Brussels in September. Prague audiences have always turned out for Vandekeybus, who says he was reluctant to mount a "greatest hits" show. "I didn't want anything special, but everyone said you must do something," Vandekeybus says with a self-conscious laugh.

Ultima Vez began in 1986 as a collaboration between a twentysomething Vandekeybus and a band of dancers in Madrid. They took Ultima Vez (the "last time") as their name, with Vandekeybus and his creative vision at the helm.

That vision hit hard — literally. Vandekeybus' first work with Ultima Vez was titled What the Body Does Not Remember, a piece that combined tremendous expenses of energy with strength, timing and trust to the point of near brutality. The most memorable image from the production was of dancers throwing, and ducking from, bricks. Times dance critic Anna Kisselgoff later called the piece a "stunning exploration of physical and emotional danger that made [Vandekeybus'] United States debut in 1987 so sensational."

Warm moments began to creep in between the hard drops and crashes of bodies in Ultima Vez pieces during the 1990s. Vandekeybus credits a deepening appreciation for intimacy and other art forms for the evolution of his choreography. Always a fan of photography and film, he began to incorporate short films and other media into Ultima Vez performances. Nondance elements that have appeared onstage with the dancers over the years include a man cooking eggs and a live dolphin.

With a broad canon of work that includes so many critically respected pieces, compiling a "best of" evening provided a daunting challenge. "In the beginning it was very difficult," Vandekeybus says. "At the end I took one piece of paper, wrote down the works, and that was it." Other pieces in the compilation include Bereft of a Blissful Union (1996), 7 for a Secret Never to be Told (1999) and Inasmuch as Life is Borrowed (2000).

Part of the difficulty was reducing choreography for elaborate works to the current lineup of nine dancers. "I cleaned [the program] out; I made it a bit more sober," Vandekeybus says. Rather than a full-blown replication of earlier works, he says, Spiegel is "more about the language" of his choreography.

With an ever-changing cast of dancers, some pieces are impossible to redo. For instance, works that Vandekeybus choreographed for blind dancers will be inherently altered when performed by artists with sight.

The audience for Ultima Vez has also changed over the course of 20 years. For longtime fans, Vandekeybus says, "What they get out of [Spiegel] is up to them." But, he adds, for anyone watching, the themes of pieces evolve and change should be rewarding, as "old material gets more organic" in the context of the retrospective.