Complex sentence: Paul Jennings (1799--1874) was an African-American slave owned by President James Madison, who later purchased his freedom and wrote a short memoir, a first for an occupant of the White House.
Split into simpler sentences: Paul Jennings (1799--1874) was an African-American slave owned by President James Madison. Jennings purchased his freedom and wrote a short memoir, a first for an occupant of the White House.