Eleanor of Aquitaine

Eleanor of Aquitaine was the consort of Louis VII of France, then of Henry II of England, and two of her sons (Richard and John) went on to become kings of England. Her first marriage was annulled in 1152 and she married Henry, then duke of Normandy. They each brought land and power to the marriage, but she threatened Henry's power and even urged three sons into an unsuccessful revolt in 1173. Henry stuck Eleanor in prison for fifteen years, but in 1189 she helped her son Richard ("The Lion-Hearted") to the throne, and for many years ruled in his absence.

Extra credit: Katharine Hepburn won an Oscar for playing Eleanor in the 1968 movie The Lion In Winter, opposite Peter O'Toole as Henry II.