Thomas Jefferson, (1743-1826). Third president of the US. As a member of the Virginia delegation at the meeting of the Continental Congress in Philadelphia, he was chief author of the Declaration of Independence (1776). He served as US minister in France (1785-89), secretary of state (1789-93) and vice president (1797-1801), before being elected president in 1801. His most notable achievement in office was the Louisiana Purchase (1803), which secured a vast territory for the US. After his retirement in 1809 he founded the University of Virginia.