Complex sentence: Stefan Banach (March 30,1892--August 31,1945) was a Polish mathematician who is generally considered to have been one of the 20th century's most important and influential mathematicians.
Split into simpler sentences: Stefan Banach (March 30,1892--August 31,1945) was a Polish mathematician. He is generally considered to have been one of the 20th century's most important and influential mathematicians.