Complex sentence: After his first few decades, he shared the work of producing the daily and Sunday strips with his assistant Formhals, who took over when Blosser retired and produced it alone from 1966 to 1971.
Split into simpler sentences: After his first few decades, he shared the work of producing the daily and Sunday strips with his assistant Formhals. When Blosser retired, Formhals produced it alone from 1966 to 1971.