Michael Chiklis was recruited to play Nathaniel Barnes, a former captain of the Gotham Police Department who, ahem, takes a particularly dark turn.

"It was a way of telling a parable of someone who believes so strictly in law and order that he can become a villain ... a judge, jury and executioner. It was a nod to due process and how the self righteous can become villains because they fancy themselves better than others. It was fun to be on something that I wasn't No. 1 on. I didn't have any pressure on me. It was a fun gig in a great place with great people."

https://ew.com/tv/michael-chiklis-role-call/?slide=541885bb-91c0-4507-b062-6b24bc98fb52#541885bb-91c0-4507-b062-6b24bc98fb52