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 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?