Why was Cooper acting like Mr. C in the finale?

At the Sheriff's station he was the old Cooper, talking and giving a heartfelt speech, then after he went through the doorway from then on he almost acted and talked just like Mr. C. Especially at the diner when the cowboys got in his face, he easily defeated them. Then he slowly and creepily walked toward the waitress and told her in a very cold and emotionless voice "Write the address down on a piece of paper" while pointing a gun at her.

I swear its like he was Mr. C, he was no longer very talkative and friendly like the old Cooper. He was like a good version of Mr. C, he had all the traits of him like not talking very much and sounding very cold and robotic when he did talk, but he was out for a good cause.