The Athelstan Vikings character arc was among the most intriguing, so much so that many viewers wondered how much of Athelstan's story on the show was accurate to true Norse and Viking history. The characters in Vikings are loosely based on real historical figures, including Athelstan (George Blagden). In the show, Ragnar Lothbrok and the other warriors of Kattegat take captives when raiding a monastery in England. Among them was Athelstan, who Ragnar took home as a slave but later inducted into his family. While characters like Ragnar, and indeed Athelstan, are based on real people, the true story is complex — especially since Athelstan shares a name with an ancient English king.
https://screenrant.com/vikings-show-athelstan-real-life-mythology-what-happened/