The reason for Steve Ballmer's retirement is he wants to get into the acting field. He greatly expressed his desire to be the next Batman in the Man of Steel Sequel. Although Steve Ballmer may not fit the role very well, he said will try his very best. He is asking Bill Gates to star in the movie as well. It is unknown who will replace Ballmer as CEO as Microsoft, however, some indications suggest either Grumpy Cat or Psy from Gangman Style.