How to attach camera's rotation to the character and make it move softly?

I want the camera to turn when the character does, camera will be completely autonom, I mean player will have no control over it. When character turns 180 degree camera follows, but not harshly, it just softly turns. So I don’t want the camera to be like a simple attachmen to character but to follow it softly by a certain distance all the time.
@ClockworkOcean