Bernstein, BURN styn, Leonard (1918-1990), was an American conductor, composer, and pianist. He ranks among the most famous figures in American music of the 1900's. Bernstein served as musical director of the New York Philharmonic Orchestra from 1958 to 1969, the first American to hold that position. During this period, the orchestra's prestige increased greatly. Bernstein often performed as solo pianist with the orchestra while conducting at the same time.