Two months later, Valeant announced a hostile $45.6 billion stock-and-cash bid for Allergan. Allergan's stock surged. In short order, Mr. Ackman had made a profit of $1 billion. But Allergan fought back and found a white knight in Actavis, a Dublin-based pharmaceutical company, which agreed to buy Allergan for $66 billion. Because Mr. Ackman still owned his Allergan shares, his profit on them rose to around $2.6 billion after Actavis bought Allergan.