Complex sentence: Altiero Spinelli (1907--1986) was an Italian citizen and advocate of European federalism; sometimes referred to as one of the "godfathers of European Union" due to his strong influence on the first few decades of post-World War II European integration.
Split into simpler sentences: Altiero Spinelli (1907--1986) was an Italian citizen and advocate of European federalism. He is sometimes referred to as one of the "godfathers of European Union" due to his strong influence on the first few decades of post-War European integration.