In Season 1, the Earl objects to Ragnar wanting to raid to the West. Ragnar goes against his wishes anyway. When he returns with many riches, the Earl makes him give it all up to him. Eventually the Earl does allow Ragnar to raid to the West however this still causes conflict. This escalates into a duel to the death between Ragnar and Earl Haraldson.
(Photo Credit: History Channel, Metro-Goldwyn-Mayer Studios Inc.)