Complex sentence: Born in 1775, Isaac was the third son of Ursula and Great George, who rose from foreman of labor to become overseer of Monticello in 1797--the only slave to reach that position.
Split into simpler sentences: Born in 1775, Isaac was the third son of two important members of the Monticello slave labor force. His father, known as Great George, rose from foreman of labor to become overseer of Monticello in 1797--the only slave to reach that position.