Margaret I (, , , ), (March 1353 – 28 October 1412), was Queen of Denmark, Norway and Sweden and founder of the Kalmar Union, which united the Scandinavian countries for over a century. She acted as queen regnant of Denmark, although in those days it was not the Danish custom for a woman to reign. Her title in Denmark was derived from her father King Valdemar IV of Denmark. She became Queen of Norway and Sweden by virtue of her marriage to King Haakon VI of Norway.