Complex sentence: Chappuis was rescued by an Italian partisan, Aldo Comucci, a 21-year old who was in charge of one of the many underground groups operating in the area.
Split into simpler sentences: Chappuis was rescued by an Italian partisan, Aldo Comucci. Comucci was 21 years old at the time and was in charge of one of the many underground groups operating in the area.