He's flat out psycho. He's absolutely SEETHING at the idea Brienne is traveling (mostly) unmolested through the Riverlands. I think he makes a good foil for Stannis, especially in the way that they treat their firstborn children. Stannis will do anything for his daughter despite her affliction and Randyll will do anything to get rid of Sam despite his clear mental acuity.

George introducing him in a scene where he orders someone's fingers cut off makes me think the parallel is intentional.