Sven

Sven grows up alongside Uhtred as a boy at Bebbanburg, the son of the warrior Kjartan, quick to sneer and quicker to cruelty. A childhood accident costs him an eye and leaves him marked, bitter, and hungry to prove himself worth more than the mockery he draws. He watches Uhtred with open resentment.

He's the show's early lesson that grudges in this world don't fade — they calcify. Ertvaag plays him without any bid for sympathy, just wounded pride curdled into menace, so that every later encounter with Uhtred carries the weight of that first humiliation. A small role that quietly seeds a lasting enmity.