Say there are men on second and third with one out. So the pitcher intentionally walks a batter to load the bases and set up a possible double play. Maybe the pitcher didn't want to pitch to a good batter anyway.

Who makes the decision for an intentional walk? Does the pitcher make this decision on his own? Or is it somehow communicated to him by a manager or a coach? Or is it true that a pitcher makes this decision some of the time, but the manager or coach can order him to walk a particularly dangerous batter, or pitch to a certain, presumably weak, one?