Styrbjarnar þáttr Svíakappa (The Tale of Styrbjörn the Swedish Champion) is a short story, a þáttr on the Swedish claimant and Jomsviking Styrbjörn the Strong preserved in the Flatey Book (GKS 1005 fol 342-344, ca 1387-1395).
It is inserted together with Hróa þáttr heimska in the description of Olaf Haraldsson's wooing of the Swedish princess Ingegerd Olofsdotter. Their purpose appears to be to present the Swedish court, its traditions and Þorgnýr the Lawspeaker.
Kings' sagas (Icelandic: konungasögur, Nynorsk: kongesoger, -sogor, Bokmål: kongesagaer) are Old Norse sagas which principally tell of the lives of semi-legendary and legendary (mythological, fictional) Nordic kings, also known as saga kings. They were composed during the twelfth through the fourteenth centuries, primarily in Iceland, but with some written in Norway.
Kings' sagas frequently contain episodic stories known in scholarship as þættir, such as the Íslendingaþættir (about Icelanders), Styrbjarnar þáttr Svíakappa, Hróa þáttr heimska, and Eymundar þáttr hrings (about people from elsewhere).
Hróa þáttr heimska or the Tale of Roi the Fool is a short story (þáttr) from Iceland about a Dane called Hrói the Fool who is helped in a legal dispute by the wise old Swede Þorgnýr the Lawspeaker, and which takes place in the late 10th century. It is preserved in two versions of which one (HróFlat) is found in Flatey Book (GKS 1005 fol 344-348, ca 1387-1395) and the second one (Hró AM 557 4°) in the Skálholtsbók (AM 557 4° 41r-42v, ca 1420-1450) in Copenhagen.
In the version of Óláfs saga helga which is found in the Flatey Book, it is inserted together with Styrbjarnar þáttr Svíakappa in the description of Olaf Haraldsson's wooing of the Swedish princess Ingegerd Olofsdotter. Their purpose appears to be to present the Swedish court, its traditions and Þorgnýr the Lawspeaker.