William and MaryThe phrase William and Mary usually refers to the joint sovereignty over the Kingdoms of England and Scotland of King William III and his wife Queen Mary II. Their reign commenced with the Glorious Revolution of 1688. Mary died in 1694 after which William ruled alone until his death in 1702.
Their rule was the only period in British history in which "joint sovereigns" with equal powers were allowed to reign. Usually, the spouse of the monarch has no power and is simply a consort.