Yes, 'The Northman' is based on a true story. It draws inspiration from Norse sagas, which were ancient tales passed down in Scandinavian culture. These sagas often contained elements of real historical events and figures, and 'The Northman' takes those and weaves them into a cinematic narrative.
The Northman is mostly a work of imagination. It weaves together elements of folklore and legend to create a captivating narrative that isn't rooted in factual history.
The revenge aspect in 'The Northman' has roots in true Viking stories. In Viking society, if a man's father was killed, like in the movie, it was his duty to avenge him. The religious beliefs depicted, such as their worship of Norse gods, are also based on historical facts. Their belief in an afterlife and the idea of Valhalla were important parts of their culture. The movie also shows the Viking raids, which were a common occurrence in history. They would sail to other lands, raid for resources, and this is shown in the movie's narrative.