Complex sentence: William Foster Apthorp (1848--1913) was a graduate of Harvard College, where he had studied piano, harmony, and counterpoint with the institution's first professor of music, the composer John Knowles Paine.
Split into simpler sentences: William Foster Apthorp (1848--1913) was a musician. He was born in 848 and graduated from Harvard College, where he studied piano, harmony, and counterpoint with the institution's first professor of music, the composer John Knowles Paine.