King is the title given to a male monarch in a variety of contexts. The female equivalent is queen regnant (while the title of queen on its own usually refers to the consort of a king).
In the context of prehistory, antiquity and contemporary indigenous peoples, the title may refer to tribal kingship. Germanic kingship is cognate with Indo-European traditions of tribal rulership (c.f. Indic rājan, Gothic reiks, and Old Irish rí, etc.)