Complex sentence: Upon his death in 1985, Dr. Napolitano was succeeded by Dr. Neil Stern, who was Acting President from 1985 to 1987, and then by Dr. Keith Asplin, who served as President from 1987 through 1989.
Split into simpler sentences: Upon his death in 1985, President Napolitano was succeeded by Dr. Neil Stern, who had been Acting President from 1985 to 1987. President Stern was then succeeded by Dr. Keith Asplin, who served from 1987 through 1989.