Tommy (Season 3 spoilers)

He started out as quite a cool guy and thought the character had potential to be a good right-hand-man to Frank. I particularly enjoyed the scenes where he violently threatened the Child Welfare worker to help Frank.
But as soon as he executed those sheep I hated him. Not only was it cruel to the animals but the sheep farmer also. After that he just got worse and worse and the dramatic character change, which all felt a little bit sudden and rushed, was not good. I just think they could have used this character in a better way rather than turning him into an arch rival to Frank.