Bill Ackman

American investor

Also known as: William Albert Ackman

Written byAdam Volle

Fact-checked byThe Editors of Encyclopaedia Britannica

Updated: Mar. 18, 2025

Bill Ackman in 2024.

William Albert “Bill” Ackman (born May 11, 1966, Chappaqua, New York, U.S.), is an American billionaire hedge fund manager. Ackman is the founder and chief executive officer (CEO) of Pershing Square Capital Management. Throughout his career, Ackman had a reputation as an activist investor—a shareholder who acquires significant stakes in companies to advocate for change in how they are run. But in 2022, he publicly swore off this approach. In 2023 Ackman gained mainstream attention for doggedly criticizing the responses of Harvard University and other schools to student protests against Israel.

Early life and education

Ackman is the second of two children born to Lawrence D. Ackman, head of a real estate brokerage firm, and Ronnie I. Ackman (née Posner). He grew up in Chappaqua, an affluent hamlet in Westchester County, and graduated from Horace Greeley High School. He was accepted into Harvard and majored in social studies. For his senior thesis, he compared Harvard admissions quotas for Jewish students in the 1920s to quotas for Asian Americans in the 1980s. During his studies, he chanced upon a copy of Benjamin Graham’s 1949 how-to book The Intelligent Investor. The book had a powerful effect on Ackman, convincing him to pursue a career in investing.

What is a hedge fund?

Investors looking to generate high returns sometimes turn to hedge funds, which use various strategies (such as short selling, leverage, and derivatives trading) to try to outperform the market. These pooled funds are generally open only to sophisticated investors who can handle higher risk and less regulation than traditional mutual funds. Hedge funds are managed by companies that make day-to-day investment decisions. Although these management companies are often colloquially called hedge funds, the term properly refers to the investment vehicle itself.

After receiving his bachelor’s degree from Harvard in 1988, Ackman enrolled in Harvard Business School. While studying there, he began to experiment with investing by buying stocks with his own money. The stocks rose in value, encouraging Ackman. Six months later, he convinced classmate David Berkowitz to join him. The pair invested together until their graduation in 1992.

Gotham Partners: Launching a financial powerhouse

After graduating, Ackman and Berkowitz founded their own investment firm, Gotham Partners Management Company. The duo started with a fund of $3 million largely collected from family and friends, which they parlayed into impressive gains throughout the 1990s. In 1995, with the backing of insurance and real estate company Leucadia National Corporation, Ackman bid for Rockefeller Center when the iconic building was put up for sale. Although the attempt failed, it raised Ackman’s profile among some of Wall Street’s biggest players. That same year, Ackman married landscape architect Karen Ann Herskovitz. The couple had three daughters before separating in 2016.

Ackman and Berkowitz’s success led to additional investment from increasingly prestigious clients. In 2000, the fund’s value reached $568 million. The partners’ initial focus on undervalued stocks had gradually changed into an investment strategy centered on controlling stakes in private companies, resulting in a portfolio of largely illiquid assets.

The approach ultimately contributed to the firm’s downfall when the pair’s mismanagement of a golf course operation business nearly drove it into bankruptcy. Spooked investors withdrew their money, reducing the fund to just $300 million by the end of 2002. Ackman and Berkowitz announced their decision to liquidate Gotham Partners’ remaining assets on December 27, 2002, and close the firm.

A big bet on MBIA and regulatory scrutiny

Even as Gotham Partners was collapsing, Ackman was making a bet in 2002 that would eventually earn him a reputation as one of Wall Street’s most prescient investors. Realizing the financial fragility of major insurers that were backing collateralized debt obligations filled with subprime mortgages, Ackman shorted the stock of the Municipal Bond Insurance Association (MBIA) and purchased credit default swaps against the company’s debt, then went public with his logic in a lengthy report.

Enraged by Ackman’s actions, MBIA’s management convinced New York Attorney General Eliot Spitzer to investigate Ackman for manipulating the market, and the Securities and Exchange Commission (SEC) soon launched an inquiry. Ackman stood firm and continued to argue his case for the next five years; he was ultimately proven correct when the subprime mortgages on MBIA’s books cratered its stock in the financial crisis of 2007–08.

Pershing Square Capital Management

By the time the regulatory probes were underway, Ackman had started a new hedge fund management company, Pershing Square Capital Management. The firm began investing on January 1, 2004, with a fund of $54 million, $50 million of which came from Ackman’s former backer Leucadia National. The fund, which eschewed diversification in favor of concentrating its money in a limited number of companies that it felt were good investments, performed spectacularly well.

By buying stakes in the Wendy’s (WEN) fast-food chain and mall operator General Growth Properties, among others, and then pushing for managerial decisions that increased those companies’ stock value—sometimes arguably at the expense of those same companies’ long-term health—Pershing Square generated a return of 692% net of fees over the next 10 years (by contrast, the S&P 500 managed 132%).

Public offerings and investment strategies

On the strength of this impressive track record, in 2014 Pershing Square started another hedge fund management company, Pershing Square Holdings (PSH), which it listed on the Amsterdam Stock Exchange (now Euronext Amsterdam). PSH’s sole purpose was to mirror the investments made by Pershing Square itself. Because the new company was publicly traded, everyday investors could effectively invest their money in it, whereas that opportunity was limited to accredited investors—those with high net worths or annual income—at Pershing Square.

Challenges and controversies

From 2015 to 2018, Pershing Square lost money. One big hit came from a $1 billion short bet on Herbalife, a multi-level marketing company that Ackman accused of operating as a pyramid scheme. Legendary investor Carl Icahn took the opposite position, turning the matter into a public showdown between two of Wall Street’s best-known hedge fund managers.

The skinny on shorting a stock

Shorting a stock is essentially betting that a company’s share price will fall. In this strategy, an investor borrows shares from a broker and sells them at the current market price. The expectation is that, as the price drops, the investor can repurchase the shares at a lower cost, return them to the broker, and keep the difference as profit. But if the share price rises instead, the investor must buy back the shares at a higher price, leading to a loss.

Ackman lost the battle. His accusations nevertheless led to the Federal Trade Commission (FTC) to investigate Herbalife, but the company settled with the enforcement agency for $200 million and was required to restructure its U.S. business. Pershing Square abandoned its position in 2018, $1 billion poorer.

In 2015, Bill Ackman’s Pershing Square Capital Management invested about $3.2 billion to acquire a 9% stake in Valeant Pharmaceuticals, now Bausch Health Companies (BHC). Shortly after the investment, the drugmaker’s business practices came under scrutiny. The company had a strategy of acquiring existing drugs and then sharply raising prices to maximize profits, a move that rendered some medications unaffordable for patients. By the time Ackman sold the investment in 2017, Pershing Square had lost about $4 billion. The outcome not only affected Pershing Square’s financial performance, but also raised concerns about Ackman’s investment strategies and judgment.

But Ackman rebounded. Declaring at the beginning of 2018 that he was going back to basics, Ackman led Pershing Square Holdings to a 58.1% return in 2019, making the portfolio one of the best-performing hedge funds in the world. In March 2020, Ackman correctly predicted that the COVID-19 pandemic would have a disastrous effect on the stock market and directed Pershing Square to take out $27 million in credit protection. The move netted the company an outsize payday of $2.6 billion.

Personal life and public engagements

In January 2019, Ackman married Neri Oxman, an Israeli-American designer and professor at the MIT Media Lab at the Massachusetts Institute of Technology (MIT). Later that year the couple had a daughter.

On October 7, 2023, the Palestinian militant group Hamas launched an attack on Israel, taking 240 Israeli civilians hostage and killing more than 1,200. Several undergraduate student groups at Harvard released a statement declaring the state of Israel “entirely responsible for all unfolding violence” because of its occupation of the Gaza Strip.

Ackman publicly called for the names of all the students involved with the statement so that they could be blacklisted, then campaigned to remove Harvard University President Claudine Gay from her position for not doing enough to curb what he considered to be antisemitic activity on his alma mater’s campus. When Republican activists later alleged that Gay had plagiarized some parts of her past works, Ackman amplified those accusations. Gay announced her resignation on January 2, 2024.

Ackman’s quest to discredit Gay led to an unwelcome focus on himself and his family. On January 3, 2024, Business Insider reported that Oxman, Ackman’s wife, had plagiarized parts of her own dissertation, leading her to apologize a day later. Ackman responded by declaring his intention to have the works of all MIT faculty members and Business Insider reporters reviewed for plagiarism.

In feuding with Harvard and other schools, Ackman began making common cause with right-wing politicians and activists long antagonistic toward the U.S. university system, taking up their criticism of diversity, equity, and inclusion (DEI) initiatives and other policies. On April 24, 2024, he announced he would not be voting a second time for President Joe Biden. In July he endorsed Donald Trump, for whom he had previously voted in 2016.

New investment initiatives

Meanwhile, Ackman had been working on a new project: Pershing Square USA, a closed-end equity fund. It was designed to mimic Pershing Square Capital Management’s investment strategy while being publicly traded on a stock exchange, similar to Pershing Square Holdings, but this time on the New York Stock Exchange (NYSE). Media analysts theorized that Pershing Square USA’s initial public offering (IPO) might raise as much as $25 billion, more than doubling the financial assets under Ackman’s purview.

Closed-end vs. open-end funds

Closed-end funds raise a fixed amount of capital through an initial public offering (IPO) and then trade on an exchange like stocks. Their share prices fluctuate based on supply and demand, which means they can trade at prices above or below the value of their underlying assets.

Open-end funds, such as mutual funds, continuously issue and redeem shares at their net asset value (NAV). Investors buy shares directly from the fund company, and the price always matches the value of the fund’s holdings.

As the date of the IPO neared, however, it became clear that there was less interest in the fund among investors than was supposed, and Ackman was forced to revise his expectations for the launch downward as low as $2 billion. On July 30, 2024, days before the stock was to debut, he canceled the IPO, promising to “report back once we are ready to launch a revised transaction.”

Adam Volle