Complex sentence: Carl Kiefert (c.1855--1937) was a composer and spent much of his career conducting at the Hippodrome and other London theatres, and orchestrated several West End musicals early in the 20th century, especially those of Lionel Monckton, and later several Broadway musicals.
Split into simpler sentences: Carl Kiefert (c.1855--1937) was a composer and spent much of his career conducting at the Hippodrome and other London theatres. He orchestrated several West End musicals early in the 20th century, especially those of Lionel Monckton, and later several Broadway musicals.