Abram Petrovich Ganibal

Great grandfather of Alexander Pushkin, Ganibal, was brought from (probably) Ethiopia at the age of 7 because children of noblemen were taken as hostages in case their fathers misbehaved. (Wikipedia quote, warning for rape: "Ganibal's sister Lahan was taken into captivity at the same time but was so cruelly raped that she died during the voyage.")

I can't find out why, but he was requested by Russians, ransomed to them and was eventually adopted by Peter the Great and was his valet on journeys and military campaigns.  

He was taught languages, geometry and mathematics before he was sent to Metz, France, to study engineering and mathematics. In France he befriended Enlightenment thinkers and in a war against Spain rose to the rank of captain before he returned to Russia.

"After the death of Peter in 1725, Ganibal was exiled to Siberia in 1727, some 4,000 miles to the east of Saint Petersburg. He was pardoned in 1730 for his skills in military engineering. After Peter's daughter Elizabeth became the new monarch in 1741, he became a prominent person at her court, rose to the rank of major-general and became superintendent of Reval (now Tallinn, Estonia) a position he held from 1742 to 1752." (During his exile he was also sent to Chinese border, to "measure the Great Wall.")

His first wife was forced to marry him and when he found out she was cheating on him he had her imprisoned in horrible conditions for 11 years (after which she was forced to join a convent). While still legally married to her, he married another woman with whom he had ten children, one of which was Alexander Pushkin's grandfather. 

He is now best known as the great grandfather of Pushkin who wrote an unfinished novel on him, Peter the Great’s Negro.

Wiki and another source.