Benjamin Banneker -- author, scientist, mathematician, farmer, astronomer, publisher and urban planner -- was descended from enslaved Africans, an indentured English servant, and free men and women of color. His grandmother, Molly Welsh, was an English dairy maid who was falsely convicted of theft and indentured to a Maryland tobacco farmer. After working out her indenture, Welsh rented and farmed some land, eventually purchasing two African slaves whom she freed several years later.
In violation of Maryland law, Welsh wed one of her former slaves, Bannke or Bannaka, said to be the son of a chief. Their daughter Mary also married an African -- a man from Guinea who had been enslaved, baptized as Robert, and freed -- who took Banneker as his surname upon their marriage. In 1731, they named their first child Benjamin.
Young Benjamin grew up in Baltimore County, one of two hundred free blacks among a population of four thousand slaves and thirteen thousand whites. He was taught to read by his grandmother Molly, and briefly attended a one-room interracial school taught by a Quaker. He showed an early interest in mathematics and mechanics, preferring books to play.
At the age of 22, having seen only two timepieces in his lifetime -- a sundial and a pocket watching -- Banneker constructed a striking clock almost entirely out of wood, based on his own drawings and calculations. The clock continued to run until it was destroyed in a fire forty years later.
Banneker became friendly with the Ellicott brothers, who built a complex of gristmills in the 1770s. Like Banneker, George Ellicott was a mathematician and amateur astronomer. In 1788, with tools and books borrowed from Ellicott, Banneker nearly accurately predicted the timing of an eclipse of the sun, discovering later that his minor error was due to a discrepancy in his expert sources rather than a miscalculation on his part.
In 1791, Banneker accompanied Major Andrew Ellicott to the banks of the Potomac to assist him in surveying the new federal city that would become the nation's capital. A notice first printed in the Georgetown Weekly Ledger and later copied in other newspapers stated that Ellicott was "attended by Benjamin Banneker, an Ethiopian, whose abilities, as a surveyor, and an astronomer, clearly prove that Mr. Jefferson's concluding that race of men were void of mental endowments, was without foundation."
In 1792, Banneker published an almanac, based on his own painstakingly calculated ephemeris (table of the position of celestial bodies), that also included commentaries, literature, and fillers that had a political and humanitarian purpose. The previous summer, he had sent a copy of the ephemeris to Thomas Jefferson, along with a letter in which he challenged Jefferson's ideas about the inferiority of blacks.
Between 1792 and 1797, Banneker published six almanacs in twenty-eight editions. He continued to live alone, selling off and renting his land, then giving the rest to the Ellicotts in exchange for a small pension. He died in 1806. On the day of his burial, his house and its contents (including his clock) caught fire and burned to the ground.
(Source: http://www.pbs.org/wgbh/aia/part2/2p84.html )