When a tyro assistant conductor, aged just twenty-five, filled in for the ailing Bruno Walter at a Carnegie Hall performance of the New York Philharmonic in 1943, the concert was so captivating to a public that listened on nationwide radio that The New York Times praised it on its front page. The newly-arrived star conductor’s father, weeping backstage with equal parts pride and disbelief, was heard to remark of his progeny, “How was I supposed to know that he was Leonard Bernstein?”

Or so claims Bernstein himself, as played by Hershey Felder in the multi-faceted one-man play with music Maestro (at 59E59 Theaters through Oct. 16). Felder wrote the play, which enables him to segue from one character and accent to another as he retells the life of Bernstein with evident love and fascination, both of which are easy to share. It’s pleasing to think of the leonine, imperious New York monument as an uncertain young sprout growing up in Lawrence, Massachusetts with a devout father who was given a piano by a crazy sister and parked it in the hallway where the boy “got curious [and] went over to touch a note.” After a year of lessons, Leonard’s piano teacher declared she could no longer help him: he was better than she was. But Leonard’s father, a Russian immigrant, believed music would take the boy farther from God and the Talmud. “My son is not going to be a klezmer!” the older man exclaimed.