The list of Norwegian kings is traditionally throught to begin in 872 with the battle of Hafrsfjord, after which victorious King Harald Fairhair merged several petty kingdoms into that of his father. Harald's realm was later to be known as the Kingdom of Norway. Now existing continuously for over 1,100 years, the Kingdom of Norway is one of the oldest states of Europe.

Harald Fairhair - Wikipedia

Here is the full list of Harald’s sons according to Snorri Sturluson's Heimskringla:

Children with Åsa, daughter of Håkon Grjotgardsson, Earl of Lade:
• Guttorm Haraldsson, king of Rånrike
• Halvdan Kvite (Haraldssøn), king of Trondheim
• Halvdan Svarte (Haraldssøn), king of Trondheim
• Sigrød Haraldssøn, king of Trondheim

Children with Gyda Eiriksdottir:
• Ålov Årbot (Haraldsdøtter)
• Rørek Haraldssøn
• Sigtrygg Haraldssøn
• Frode Haraldssøn
• Torgils Haraldssøn – identified as "Thorgest" in the (dates not correct) Irish history

Children with Svanhild, daughter of Eystein Earl:
• Bjørn Farmann, king of Vestfold
• Olaf Haraldssøn Geirstadalf, king of Vingulmark, later also Vestfold
• Ragnar Rykkel

Children with Åshild, daughter of Ring Dagsson:
• Ring Haraldsson
• Dag Haraldsson
• Gudrød Skirja
• Ingegjerd Haraldsdotter

Children with Snøfrid, daughter of Svåse the Finn:
• Halfdan Halegg or "Long-leg", was executed with the Blood eagle ritual by Torf-Einarr detailed in the Orkneyinga saga and Heimskringla
• Gudrød Ljome
• Ragnvald Rettilbeine
• Sigurd Rise

Other children:
• Ingebjørg Haraldsdotter