Wu was the concubine of Emperor Taizong. After his death, she married his successor his ninth son, Emperor Gaozong, officially becoming Gaozong's huanghou. translated as ("wife", or "empress consort") although having considerable political power prior to this. After Gaozong's debilitating stroke in 660, Wu Zetian became head of the court, a position equal to the emperor's until 705 (she was kinda awesome)
the Zhou dynasty rose
Wu Zetian was the unofficial empress of this dynasty.