Thelonious Jaha is a major character in the first, second, third, and fourth seasons. He is portrayed by starring cast member Isaiah Washington and debuts in the series premiere. Jaha was the last Chancellor of the Council that governed the Ark. As the Chancellor, Jaha had a major role on the Ark, that brought on many hard decisions and challenges, such as ending the lives of hundreds of people in order to save thousands, or choosing to stay behind on the Ark to ensure that some of humanity can return to their home planet.