Daniel Acker/Bloomberg News

William A. Ackman has set his sights on another high-profile consumer products giant.

The hedge fund manager confirmed to DealBook on Thursday that his hedge fund, Pershing Square Capital Management, has taken a big stake in Procter & Gamble.

The disclosure followed a notice from the Federal Trade Commission that essentially allowed Pershing to take a stake in the 175-year-old maker of Gillette razor blades and Tide detergent.

Shares in Procter & Gamble closed up 3.75 percent percent on Thursday, at $63.70. It had risen even higher earlier in the day, its stock nearing its 52-week high.

In some ways, Procter & Gamble makes a tempting objective for activist investors, as its stock was down nearly 5 percent for the 12 months through Wednesday. But it is also a massive target for any one shareholder to take on: As of Thursday’s close, Procter & Gamble was valued at nearly $175 billion.

Still, Mr. Ackman said in a telephone interview on Thursday that Pershing will be a major Procter & Gamble shareholders.

“We think it’s an undervalued stock,” he said. “We think there’s a lot of great opportunity there.”

Mike Cassese/Reuters

A spokesman for Procter & Gamble, Paul Fox, said in a statement: “We welcome investment in our company. We are focused on creating shareholder value by executing on our plan to deliver top and bottom line growth through our $10 billion cost savings program, renewing our focus on innovation, pricing initiatives and improved execution, and reallocating resources to invest in the highest return opportunities.”

At the moment, it’s unclear what Mr. Ackman will do, though he isn’t expected to be a passive investor.

Over much of the past decade, the hedge fund manager has established himself as a top activist shareholder. Among his most recent victories was at the Canadian Pacific Railway, where he took control of the board in May after an acrimonious proxy contest.

While Mr. Ackman declined to comment on his plans for Procter & Gamble, one can certainly speculate on his potential moves. One may be call for a shake-up Procter & Gamble’s management, one of the most oft-used tactics in the activist toolbox.

Another is to call for the sale of several divisions to bolster shareholder value, something that some analysts have called for. It is a tactic he successfully employed at the company formerly known as Fortune Brands, an awkward combination of alcoholic beverages like Jim Beam, a home security division and a collection of golf brands like Titleist.

Fortune sold its golf division to the parent of Fila in 2011 for $1.2 billion, and later divided its liquor and home security divisions into separately traded companies.

Shares in Beam Inc. have since risen 36 percent, and shares in Fortune Brands Home & Security have surged nearly 70 percent.

Other activist investments have not quite yielded what Mr. Ackman has wanted. He lost a proxy contest at the Target Corporation three years ago, after pushing the retailer to spin off its real-estate holdings and sell its credit-card receivables.

And he is on the board of J. C. Penney, which has been struggling to turn itself around after pursuing an ambitious reinvention campaign under Ron Johnson, the former head of Apple‘s retailing operations.