Erketü Qatun (Mongolian:ᠡᠷᠬᠡᠲᠦᠬᠠᠳᠤᠨ; means Powerful Queen) (ca. 1551–1612), also referred to as the Third Lady (Chinese: 三娘子） , was an influential member of the Borjigin clan in late 16th century and early 17th century Mongolia. Her real name is unknown, only being remembered by a title bestowed upon her. She was the wife of four subsequent leaders of the Tümed, and her pro-Ming Empire views kept the longest peace between the two competing powers. She is also known as Sanniangzi.