Pfizer and Allergan have entered into a definitive merger agreement under which Allergan will acquire Pfizer in a stock transaction valued at approximately $160 billion. Pfizer and Allergan’s businesses will be combined under Allergan plc, which will be renamed Pfizer plc. Although Allergan is buying Pfizer, Pfizer will retain control of the company. Former Pfizer stockholders will hold approximately 56% of the combined company and Allergan shareholders will own approximately 44%.   The combin...