The first Kings attested in contemporary sources are those mentioned in the Vita Ansgari. However, very little is known about the extent of their rule. The first king attested in more than one source was Eric the Victorious, who lived around 970–995. He was succeeded by his son King Olof Skötkonung (late-960s – circa 1020), who also is the first king we know ruled over both parts of Svealand and Götaland. Earlier kings often only ruled over parts of the present territory of Sweden, and so their validity as 'kings of Sweden' may be questioned. However, according to the Viking sagas, those territories were sometimes united under a single ruler.
In sources such as Heimskringla and Ynglinga saga there appear early Swedish kings who belong in the domain of mythology. From about the 6th century, these kings are gradually succeeded by semi-legendary kings with at least partial claim to historicity, who were all depicted as descendents of the House of Ynglings/Scylfings, either in direct royal line, or through the House of Ragnar Lodbrok and the house of Skjöldung (Scylding).
A historical basis of some of the mythological kings was one of the last of Thor Heyerdahl's archeo-anthropological theories, as in The Search for Odin. Such suggestions are generally considered speculative, not scientific, but while there is no historiographical tradition that would confirm the historicity of Swedish kings prior to the 6th century, it is safe to assume that the Suiones, as a tribe mentioned by Tacitus in the 1st century AD, did have kings (Common Germanic *kuningaz) during the prehistoric period.
The genealogy is traced to Odin himself (as are the Anglo-Saxon royal genealogies). Odin is euhemerised as an Asian noble with a genealogy going back to the Trojans. King Fjölnir, the 4th generation after Odin, in the Grottisongr is named a contemporary of Caesar Augustus, placing him late in the 1st century BC. The kings following Fjölnir based on internal chronology would then span the 1st to 7th centuries AD. The later Yngling kings of the Vendel Period (6th to 7th century) may well correspond to historical rulers, even if biographical detail from the Heimskringla has to be considered legendary; the kings Egil, Ottar and Ale are also attested in Beowulf. After Ingjald, Snorri does not relate any further stories of Swedish kings, and follows the descendants of the house to Norway.