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.

Mark Zuckerberg

Zuckerberg does not invest in the traditional sense — he builds and holds. He controls Meta through a dual-class share structure that gives him roughly 54% of voting power with less than 15% economic ownership, meaning no board or shareholder can remove him regardless of how the stock performs.

He has made massive bets inside Meta — on mobile (right), Instagram (very right), WhatsApp (right), VR/metaverse (wrong so far), and AI (still playing out). His investment thesis is that social connectivity is a fundamental human need and whoever owns the infrastructure owns everything.

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.

Mark Zuckerberg

Zuckerberg thinks in decades, not quarters. His core belief is that the most important technology of the next century is whoever connects people at scale — first through social networks, then through AR/VR, and now through AI agents.

He is willing to absorb years of losses on bets he believes in. He says he would rather make a big bet and be wrong than be timid and miss the next platform shift.

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.

Mark Zuckerberg

Zuckerberg spent $36 billion on Reality Labs — VR and AR — between 2019 and 2023, with little to show in revenue. He did not flinch.

He also bet Facebook's entire business model on going mobile in 2012, acquired Instagram for $1 billion when it had 13 employees and no revenue, and has held through Congressional hearings, advertiser boycotts, and multiple existential challenges from competitors. His personal financial risk is minimized by his dual-class share structure — he controls voting power regardless of what the stock does, so no board or activist investor can force his hand.

He can lose at scale for as long as he believes the thesis.

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.

Mark Zuckerberg

He wore the same grey t-shirt every day for years — he said it reduced decision fatigue. He trains MMA and Brazilian jiu-jitsu seriously, competing in actual tournaments.

He wakes up early, spends mornings with his family, and starts work at 8am. He has spoken about designing his schedule to protect creative work in the mornings.

He reportedly does not check email first thing.

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.

Mark Zuckerberg

Acquiring Instagram for $1 billion in 2012. Instagram was growing fast, potentially threatening Facebook's dominance with younger users.

Facebook bought it. It now generates an estimated $40-60 billion in annual revenue.

Many consider it the best acquisition in tech history on a return basis — $1 billion in for what became a $100B+ asset.

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.

Mark Zuckerberg

The metaverse bet. From 2021 to 2023, Meta spent over $50 billion on Reality Labs — its VR and metaverse division — and generated minimal revenue.

The division lost $16 billion in 2023 alone. Meta's stock fell nearly 75% at its 2022 trough.

Zuckerberg was widely mocked, called the metaverse a disaster, and faced enormous internal and external pressure. He then pivoted hard to AI and the stock recovered.

The metaverse losses remain one of the most expensive executive vanity projects in corporate history.

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.

Mark Zuckerberg

Mark Zuckerberg launched Facebook from his Harvard dorm in February 2004. By the end of 2004, the site had 1 million users.

He turned down a $1 billion acquisition offer from Yahoo in 2006. By 2012, Facebook went public at a $104 billion valuation — the largest tech IPO in history at the time.

The stock immediately fell 50%. It then recovered to become one of the most valuable companies in the world.

In 2012, Facebook acquired Instagram for $1 billion (now worth over $100 billion). In 2014, it acquired WhatsApp for $19 billion.

In 2021, he rebranded the parent company to Meta to signal a pivot to the metaverse — a move that cost over $50 billion in investment and destroyed significant shareholder value before the company course-corrected toward AI.

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.

Mark Zuckerberg

Meta Platforms (CEO and controlling shareholder — holds majority voting control through supervoting shares). Key acquisitions: Instagram (2012, $1B), WhatsApp (2014, $19B), Oculus VR (2014, $2B).

Chan Zuckerberg Initiative (co-founded with wife Priscilla Chan — philanthropic LLC).

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.

Mark Zuckerberg

Harvard University — studied computer science and psychology. Dropped out in 2004 to move Facebook to Palo Alto.