Complex sentence: On a whim, Hart, who had never written a song, approached Portnoy, who had never written for the theater and, together, they set out to compose the words and music for the musical named "Preppies".
Split into simpler sentences: On a whim, Hart, who had never written a song, approached Portnoy, who had never written for the theater. Together they set out to compose the words and music for the musical named "Preppies".