Kaplan—whose older brother was the composer Joseph Brooks, who won an Academy Award for “You Light Up My Life”—was an indifferent music student while growing up. But the story goes that in 1965, while he was working in finance, he heard Mahler's Symphony No. 2 (“Resurrection”) and became obsessed with it. Two years later he founded Institutional Investor, an industry magazine that became enormously successful; it grew into a multimedia company that he sold in 1984, reportedly for more than $70 million.

In 1981, Kaplan hired Charles Bornstein (BM '74, orchestral conducting) to teach him to conduct. Fast forward a year, when, to celebrate the 15th anniversary of the magazine, Kaplan rented Avery Fisher Hall and hired the American Symphony Orchestra to perform under him, which it agreed to do with the proviso that it would be a private concert and there would be no publicity. An invited Village Voice critic broke the embargo with a glowing review (he wrote that it was “one of the five or six most profoundly realized Mahler Seconds” in the previous quarter century), and an unlikey conducting career in which Kaplan would lead more than 60 orchestras around the world—always in Mahler's Second— began. He also made two recordings of the piece, first with the London Symphony and then the Vienna Philharmonic.

Eventually Kaplan would serve on the boards of Carnegie Hall and WNYC, where for a long time he hosted a radio show called Mad About Music. His affiliation with Juilliard began in 2000, when he taught the first of many Evening Division courses on Mahler; he was scheduled to teach one on Mahler's Second in September. In 2001, Kaplan, who became a Mahler collector and publisher (of facsimile editions of Mahler scores) as well as a scholar, gave a doctoral forum here called The Debate Over Interpretation in Mahler's Second Symphony. Kaplan is survived by his wife, four children, and eight grandchildren.