200px|thumb|right|The [[Uppland Rune Inscription 861|Norsta Runestone (U 861) on the drive of Wik Castle outside Uppsala was probably made by Sweyn and his family, as it mentions two people called Sweyn and Mær (mentioned in the accusative form Møy). It is the only existing mention of a woman named Mær ("maiden") besides the mention of Sweyn's sister Mær in Hervarar saga, and it is contemporary with Sweyn.]]
Blot-Sweyn () was a Swedish king c. 1080, of disputed historicity, who was said to have replaced his Christian brother-in-law Inge as King of Sweden, when Inge had refused to administer the blót (pagan sacrifices) at the Temple at Uppsala. There is no mention of Sweyn in the regnal list of the Westrogothic law, which suggests that his rule did not reach Västergötland.
However, Inge did not permit the people to follow the old ways, unlike his father Stenkil. The Swedes reacted strongly and asked Inge to either comply with the old traditions or abdicate. When Inge proclaimed that he would not abandon Christianity, the people pelted him with stones and chased him away.
This legend is, however, only known from the late 13th century. An account by Aelnoth of Canterbury (c. 1122) relates that an Eskillinus was killed by pagan Swedes and Geats at an unspecified time. Since he is not mentioned by the clerical historian Adam of Bremen (c. 1075), he may have flourished in the late 11th century. According to another opinion, Eskil's death is more probably dated in c. 1016, several generations before Blot-Sweyn.
Death
According to Hervarar saga, the rule of Sweyn was not to last. Before long, the Christian Inge decided to kill the pagan Sweyn:
Succession
It is possible that Inge was not immediately accepted by the stubbornly pagan Swedes of Uppland. The 13th-century historian Snorri Sturlusson wrote in the Heimskringla that Blót-Sweyn had a pagan successor who continued the sacrifices:
This "Eirik Arsale" (Erik Årsäll) is mentioned in other sources as being the son of Blot-Sweyn, but today is not considered a historical person by most historians.