Olaf II Haakonsson (1370 – August 23, 1387) is king of Denmark as Olaf II (1376–1387) and king of Norway as Olaf IV (1380–1387).

Olaf is the son of King Haakon VI of Norway and the grandson of King Magnus IV of Sweden.

His mother is Queen Margaret I of Denmark, which makes him the grandson of King Valdemar IV of Denmark.

In addition to his claim on the thrones of Denmark and later Norway, he is in the direct succession line to the throne of Sweden (but for the interposition of Albert of Mecklenburg).

He becomes king of Denmark when only five years old and later also succeeds his father as king of Norway.

For over four hundred years that follow, Norway will be ruled from Denmark, until its separation from that country in 1814.