Olaf IV Haakonsson, (1370 - August 23, 1387), King of Norway and Denmark, son of Haakon VI of Norway and Margaret of Denmark. Haakon was son of King Magnus II of Sweden and Margaret daughter of King Waldemar Atterdag of Denmark. After Olaf, no Norwegian king was to be born on Norwegian soil for more than 550 years, until prince Harald was born in 1937.

Olaf inherited the Danish throne through his mother and reigned as king of Denmark (1376-1387) as Oluf III and the Norwegian throne from his father and reigned in Norway (1380-1387) as Olav IV. Following his premature death in 1387, his mother Margaret was able to unite the three Scandinavian kingdoms in personal union under one crown, by the Kalmar Union in 1389.

Preceded by: Valdemar IV	King of Denmark	Succeeded by: Margaret I
Haakon VI	King of Norway