He charged quickly out of the gate, persuading Wendy’s to divest itself of the Canadian chain Tim Hortons. Then he got McDonald’s to sell some of its restaurants and buy back shares. It became clear that when Pershing Square announced a stake in a company, something big was going to happen, and the stock moved.

“Bill commands a room. He’s a tall guy, a good-looking guy. He draws all eyes to him when he speaks,” said Damien Park, the founder of Hedge Fund Solutions, which consults on activist campaigns but has not worked with Mr. Ackman. “Also, his ideas aren’t usually incremental in nature — asking a company to distribute cash or clean up a balance sheet. They’re usually quantum changes in a company.”

That was true of his 2007 mark on Target. In just two weeks, he raised $2 billion for a special fund to invest in just one stock. He wanted Target to sell its credit card business and restructure its real estate holdings. Target sold off part of its credit card business, but management disagreed with his real estate plan. Over the course of two years, Mr. Ackman waged a $10 million campaign to replace board members with himself and four others.

When shareholders voted against him in the spring of 2009, the defeat stung more than his reputation. By then, losses amounted to as much as 90 percent, and many investors in the special Pershing Square fund, including the fellow activist investor Daniel S. Loeb through his Third Point hedge fund, had asked for their money back.

Mr. Ackman suffered another black eye a few years later with J. C. Penney. He won a seat on its board in 2011 and handpicked Ron Johnson, the head of Apple’s retail stores, to turn around the troubled retailer. But the efforts were botched; the company went from being profitable to losing $1.4 billion in 2013. Mr. Ackman resigned from the board in the summer of 2013, selling his stake at an estimated loss of $473 million.

“Every time I see him,” said Mr. Hill at Blackstone, “I say: ‘Bill, do me a favor. Stay away from retail.’ ”

Still, Mr. Ackman notched two of his biggest hits — General Growth Properties and Canadian Pacific — over the same period, helping to offset the reputational and financial losses from Target and J. C. Penney. Pershing estimates that Mr. Ackman’s original $65 million investment in General Growth, which operated commercial properties and has been restructured into three businesses, is now worth $3.3 billion. In Canadian Pacific, Mr. Ackman has so far tripled the value of his original investment after replacing the board and forcing through a turnaround.