Complex sentence: Thomas Jefferson (April 13 (O.S. April 2) 1743--July 4,1826) was an American Founding Father who was the principal author of the Declaration of Independence and later served as the third President of the United States from 1801 to 1809.
Split into simpler sentences: Thomas Jefferson (April 13, O.S. April 2.1743--July 4,1826) was an American statesman, one of the Founding Fathers of the United States and the principal author of the Declaration of Independence. He later served as the third President of the United States from 1801 to 1809.