ember controllers are different from rails controllers in that their primary function is to provide the logic to access data from the model. In this example, the user has different first_name, last_name properties, but wants to show a full name. This is something that a controller would be used for.

ember controller

App.UserController = Ember.Object.Controller.extend({
  fullName: function() {
    return this.get("first_name") + " " + this.get("last_name");
  }
})