Ackman Amassed Allergan Stake Under Botox Maker’s Radar

Bill Ackman’s Pershing Square Capital Management LP amassed almost 10 percent of Allergan Inc. in less than two months without raising many eyebrows at the Botox-maker he’s now targeting in a hostile takeover bid.

Now, Ackman’s activist hedge fund has partnered with serial acquirer Valeant Pharmaceuticals International Inc. to buy Allergan for about $46 billion in a cash-and-stock deal. The goal is to reap savings by joining the companies’ skin- and eye-care businesses.