May 2, 1729 - November 17, 1796: Age 67
Catherine the Great was a German princess who married the heir to the Russian throne. In time, her husband ascended the throne as Tsar Peter III.
Catherine was a brilliant woman in many respects, but above all a brilliant politician. Her husband, on the other hand, was not, and in 1762 she initiated a bloodless coup. He was sent to retire in comfort on a country estate, but was killed soon after by conspirators fearing his return to power.
Although she was not Russian her son, Paul, was the legitimate heir, and she was accepted by the Russian people as their ruler. Catherine ruled Russia pretty much unchallenged for the remaining 34 years of her life. During that time she ruled competently, mediated foreign disputes, corresponded with the greatest minds of the era, took countless lovers, and brought Russia into closer alignment with the principles of the Enlightenment.
On November 16, 1796 she woke up in the morning, had her morning coffee, dismissed her lover and went into her bathroom. When she didn't come out for half an hour, her attendants called for her secretary. When his knock didn't get an answer, he went in, and found her unconscious on the floor. Doctors tried to revive her by bleeding her and raising blisters on her feet, but to no avail. She died the next evening.
Sources: Wikipedia; Forbes, Malcolm, They Went That-a-Way, Simon and Schuster, 1988.