6. Thomas Jefferson
Thomas Jefferson married his third cousin Martha Wayles Skelton Jefferson in 1772. They had six children together. Martha died on September 6, 1782 and Jefferson never remarried.
5. Albert Einstein
Albert married his second cousin Elsa in 1919, not too long after his divorce from his first wife Mileva. Elsa died in 1936 due to various health problems, and though Albert never married again he had several girlfriends until his death in 1955.