Can a person make the difference in a course of events? Marxist historians would say no, that it is material forces that influence actions. Determinist critics, too, claim that the choreographic substance makes or breaks a ballet. At the Bolshoi, though, the tradition of the individual hero was very much alive this weekend as the company wound up its seven performances of "The Golden Age" in the Kennedy Center Opera House. New casting did, in at least one instance, change what happened on stage.

Andris Liepa -- making his debut here Friday night -- dances, acts and looks very different as Boris, a young man of the people, from his predecessors in the role, Irek Mukhamedov (who combines personal reticence with spectacular outbursts of movement) and tough Yuri Vasyuchenko. Liepa is the sort of kid who could charm anyone but a viper into being a good citizen. Incapable of staying angry, the daggers that are his eyes turn to cups of wine and honey as he stares down the villain in Yuri Grigorovich's epic cartoon of a ballet about postrevolutionary Russia in the roaring '20s. He's like a big puppy, not just in his love for Rita, the virtuous nightclub dancer, but in all he does,whether it's hauling in the fishing nets down at the shore or playing a militarist in agitprop theater at a people's celebration. To the acrobatic persistence of Grigorovich's choreography, Liepa brings freshness and cheer.

As a dancer, Liepa may be a lyricist rather than a born acrobat. He has to exert himself to perform the heroic legwork that embellishes Boris' many leaps. But the effort is immaculate. (Not all the steps the different Borises perform are identical.) With his agile body, broad features and winning smile, Liepa would be slated for stardom even he didn't sport an eye-catching golden halo of hair. (Intermission conversation buzzed about whether that glint was as natural as a Russian wheat field in sunlight or the result of a bit of alchemy.)

Liepa's Rita, both Friday and Saturday night, was Lyudmila Semenyaka. Precise and passionate, she's a good match except for her refusal to look glamorous. Nina Semizorova, as the bad girl Lyuska on Saturday night, combined her predecessors' qualities in the role -- Tatyana Golikova's hard-boiled pout with Maria Bilova's flippancy.

"Golden Age" is full of the character vignettes that used to be features of Ballet Russe repertories, and the Bolshoi still has plenty of dancers who know how to make an instant impression without disrupting the main action. First and foremost was Stanislav Chasov, a Master of Ceremonies both mercurial and menacing, but there were also Aleksandr Vetrov's gung-ho sailor, Dmitri Matrakhov's wise and wicked billiards player, Aleksandr Kedrov's excited newsboy. The minor women's roles were less distinct, though Tatyana Bessmertnova as part of a modern me'nage knew how to draw attention. What we haven't been able to tell but will in the next few days is how this young Bolshoi troupe dances the classics.