Bill Ackman

Ackman is a concentrated, long-hold, activist investor. He typically owns 5–10 positions at a time — sometimes fewer.

Each one involves exhaustive research. If he's buying, he has usually already built a 100-slide deck explaining exactly what's wrong with the company and exactly what needs to change to fix it.

His style is the opposite of index investing. He wants a controlling voice at the table.

He wants to talk to the CEO. He wants the board to change.

That's the "activist" part — he's not just buying a stock and hoping it goes up. He's buying it with a plan to force the thing that will make it go up.

The strategy works until it doesn't. When the thesis is right, he wins massively.

When the thesis is wrong and he's also very public about it, the losses are spectacular.

Ken Griffin

Citadel is multi-strategy, meaning it runs many independent investment approaches simultaneously — equities, fixed income, commodities, macro, quantitative. Within each strategy, the approach is deeply research-driven and increasingly quantitative.

Griffin has built an organization that competes by having better data, better models, and better technology than rivals. He recruits aggressively from top universities and research institutions.

The edge is institutional, not personal — it is the collective intelligence of thousands of analysts and engineers working together, not one man's intuition.

Bill Ackman

Ackman's core belief is that markets frequently misprice assets when the story around them is either too negative or too complicated. He looks for businesses he can understand deeply, with a gap between what the market thinks they're worth and what he thinks they're worth.

He's talked extensively about asymmetric bets — situations where you can be wrong and lose a small amount, but right and make a lot. He believes activist investing works because most company boards are too comfortable and most CEOs have too little accountability.

He thinks public pressure, when backed by real analysis, is a legitimate tool for creating value. Whether that makes him a hero or a villain depends on which company you ask.

Ken Griffin

Griffin believes that markets are competitions between the best-informed, best-equipped participants, and that winning over time requires relentless investment in research, technology, and talent. He has said that Citadel spends more on technology than most technology companies its size.

His philosophy is not about finding one great insight — it is about building systems that generate small edges consistently, at enormous scale, across thousands of trades and hundreds of strategies.

Bill Ackman

Ackman runs highly concentrated books and uses leverage. That's the opposite of conservative.

He'll put 20–30% of the fund in a single position if he believes in it. He also uses options and credit derivatives — his March 2020 COVID hedge was built using credit default swaps, instruments most retail investors have never heard of.

He famously described his risk approach as: "I only invest when the downside is zero and the upside is unlimited" — which sounds great until you lose $4 billion on one trade. The honest version is: he's a high-conviction investor with a high tolerance for pain on the way to being right.

Ken Griffin

Griffin is known for demanding risk management and being willing to cut positions aggressively when models signal danger. The 2008 loss of 55% is the exception that proves the rule — he survived it, refined the risk systems, and the firm has been significantly more resilient since.

He uses leverage extensively, but with a risk framework sophisticated enough that most of the firm's strategies are not correlated — when one book loses, another may gain. He is also known for being very hard on underperforming managers.

Bill Ackman

Ackman has a taste for the finer things and doesn't pretend otherwise. He owns a large Manhattan apartment, he's been photographed at high-end charity events, and his social circle overlaps with New York media, finance, and political elite.

He and his second wife, Neri Oxman, have a high public profile — she's a former MIT professor and design pioneer. He gave $25 million to Harvard (his alma mater), though the relationship became famously strained in 2023 when he led a very public campaign against Harvard's president over campus antisemitism, ultimately contributing to her resignation.

He is not a guy who stays quiet about anything.

Ken Griffin

Griffin is one of the most extravagant spenders of any investor on this list, and he does not hide it. He paid $238 million for a Manhattan penthouse, the most expensive home ever sold in the United States.

He bought a $122 million mansion in Palm Beach. He owns a Boeing 767 private jet.

He has donated over $1 billion to arts, education, and political causes — the University of Chicago's economics department is named after him following a $125 million gift. He is the largest individual donor in Illinois political history.

Bill Ackman

The COVID hedge in March 2020 is the one. As markets started selling off in late February, Ackman quietly spent $27 million buying credit default swaps — basically insurance on corporate bonds defaulting if the economy collapsed.

He then went on CNBC on March 18, 2020, visibly emotional, and said "hell is coming." The market kept dropping. Three weeks later, he unwound the trade.

The $27 million had turned into $2.6 billion. That's roughly a 100x return in under a month.

He used the proceeds to buy stocks at the market bottom. He then made another fortune as markets recovered.

The whole sequence — hedge, cry on TV, buy the dip, profit — is one of the more remarkable individual trade sequences in recent hedge fund history.

Ken Griffin

2022 is the defining year. While global markets were in freefall — the S&P 500 down 18%, bonds down dramatically, most hedge funds losing money — Citadel's Wellington fund returned approximately 38%.

The firm made $16 billion in profit for its investors in a single year, the most ever made by a hedge fund in one calendar year. The strategy worked because Citadel had positioned correctly for rising inflation and rising rates — a macro call that most funds missed entirely.

The $16 billion in 2022 alone exceeded the total profits of virtually any fund over its entire history.

Bill Ackman

The Valeant Pharmaceuticals disaster is the one. Ackman built a massive position in Valeant starting in 2015, eventually owning about $4 billion worth of shares.

His thesis was that Valeant's model — aggressively raising drug prices and cutting R&D — was brilliant. Congress, journalists, and eventually the SEC had a different view.

The stock collapsed from $260 to under $10. Ackman spent months publicly defending the position, appearing on CNBC repeatedly to explain why it would recover.

It didn't. He finally sold in 2017 at a loss of approximately $4 billion.

It's the most expensive public loss in hedge fund activism history. The lesson he's cited: don't get emotionally attached to a position, and be faster to recognize when the fundamental thesis has broken.

Ken Griffin

2008 is the dark chapter. Citadel's flagship funds lost approximately 55% during the financial crisis — not because of bad trading specifically, but because of a liquidity crisis.

Citadel held positions in illiquid securities that could not be sold without moving the market against them, and redemption pressure from investors compounded the problem. Griffin was forced to suspend redemptions — meaning investors who wanted to leave could not get their money out.

He spent months rebuilding. The firm survived, but the episode forced a fundamental redesign of Citadel's liquidity management and risk controls.

Bill Ackman

Bill Ackman grew up in Chappaqua, New York, the son of a real estate finance chairman. He was a history major at Harvard — class of 1988 — then went straight to Harvard Business School.

His first venture was Gotham Partners, a real estate and value investing fund he started in 1992 with a Harvard classmate. It was a disaster.

The fund made concentrated bets on illiquid real estate and had to be wound down by 2003 under serious investor pressure and SEC scrutiny.

He didn't quit. In 2004 he launched Pershing Square Capital Management, this time with a clearer focus: take large stakes in companies, go public with his thesis, and use activist pressure to force management changes.

The approach worked. His reputation was built on detailed, public investment presentations — sometimes running 100+ slides — that became must-reads on Wall Street.

He turned activist investing into something that felt more like journalism than finance: research a company, find what's broken, publish everything, and bet heavily on being right.

Ken Griffin

Griffin grew up in Boca Raton, Florida, and showed early signs of being extremely competitive and extremely interested in markets. He enrolled at Harvard in 1986 and almost immediately started trading — he installed a satellite dish on the roof of his dorm to get live stock data, and began running convertible bond arbitrage strategies with money raised from family.

By the time he graduated in 1989, he had been profitable enough that a hedge fund manager named Frank Meyer had given him $1 million to manage.

He launched Citadel LLC in 1990 at age 22 with $4.6 million. The name came from the idea of building something fortified, defensible, and hard to breach.

He spent the 1990s building out quantitative infrastructure, recruiting mathematicians and engineers rather than traditional traders, and expanding into multiple strategies. By the 2000s, Citadel was one of the most feared names in hedge funds.

The 2008 financial crisis hit the firm hard — the flagship funds lost about 55% — but Griffin did not close. He survived, rebuilt, and came out stronger.

Bill Ackman

Pershing Square Capital Management is his flagship hedge fund, managing around $16 billion. His most famous public positions have included Canadian Pacific Railway, where he pushed successfully for a new CEO and a turnaround that made Pershing Square hundreds of millions.

He held a massive position in Valeant Pharmaceuticals from 2015 to 2017 — which will come up again. He took a huge bet on General Growth Properties during the 2008 financial crisis when no one else would touch it.

That one returned over $1 billion.

He has also done business on the other side: Pershing Square Holdings is his publicly listed vehicle on Euronext Amsterdam, which lets retail investors access his fund — unusual for a hedge fund of this size. He's been a major Burger King and Restaurant Brands International investor, and he backed Fannie Mae and Freddie Mac preferred shares in a long-running legal battle with the government.

Ken Griffin

Citadel LLC is the hedge fund business, managing approximately $58 billion. It runs multiple strategies across equities, fixed income, macro, and credit.

Its flagship Wellington and Kensington funds have produced extraordinary long-term returns — compounding at roughly 19% annually since inception. The firm has thousands of employees across multiple continents and is considered one of the most technologically sophisticated investment firms in the world.

Citadel Securities is a separate but equally important business. It is one of the largest market makers in US equities, handling approximately 25–30% of all US retail equity order flow.

When someone uses Robinhood or TD Ameritrade to buy a stock, there is a meaningful chance Citadel Securities is on the other side of that trade. This business is enormously profitable and is what made Griffin one of the wealthiest people in finance.

Bill Ackman

Harvard College, BA in History, 1988. Harvard Business School, MBA, 1992.

He's been a major Harvard donor — and major Harvard critic — throughout his career. The irony of his most public fight being with his own alma mater was not lost on anyone.

Ken Griffin

Harvard University, BA in Economics, 1989. He arrived already interested in markets and left already running a fund.

He has donated hundreds of millions to Harvard and to the field of economics broadly — the Griffin Graduate School of Arts and Sciences at Harvard was named in his honor following a $300 million gift, the largest in Harvard's history.