What does it take to build a modern-day Berkshire Hathaway?

Bill Ackman might have some ideas — and he's quietly putting them in motion.

The billionaire hedge fund manager, best known for bold bets and highly concentrated investments, has made headlines over the past few weeks, including some major buys and tariff comments.

On May 5, his Pershing Square Capital Management announced a $900 million deal to acquire 9 million newly issued shares of Howard Hughes Holdings  (HHH) , a company Ackman plans to turn into a "modern-day version of Berkshire."

Berkshire Hathaway was the conglomerate that Warren Buffett turned from a struggling textile manufacturer into a holding company owning a diverse range of businesses, including insurance, utilities, and retail. Investors see it as a model of long-term, value-oriented investing.

"Fortunately, our starting base of assets won't be a dying textile company, but a very good business," Ackman wrote on X. "We will adopt similar, long-term, shareholder-oriented principles to Berkshire, and we intend to hold the stock forever."

That same idea of buying strong businesses and holding them long-term is showing up elsewhere in Ackman’s portfolio.

Ackman’s Pershing Square oversees a highly concentrated portfolio of just 11 stock holdings.

The fund has delivered strong returns over time. It has returned 42.17% over the past three years and 149.55% over the past decade, according to data from Stockcircle.

Related: Billionaire Bill Ackman delivers frank 3-word message on tariff war

On May 22, Ackman told clients that his hedge fund bought shares of Amazon.com, Inc.  (AMZN)  last month, betting earnings will continue to grow as President Donald Trump's tariffs turned out to have less impact on consumers than expected.

Amazon is one of the world's most valuable companies with a market value of more than $2 trillion. Its business spans e-commerce, cloud computing, logistics, and digital advertising.

The stock had plummeted by over 30% after Trump's tariff announcement as investors worried about potential higher costs and weaker demand in Amazon’s global retail business.

However, Amazon CEO Andy Jassy told investors this week that tariffs have not significantly impacted consumer spending or average sales prices. And Ackman's team also thinks tariffs would not have a "material impact on the earnings in the retail business."

Pershing Square's Chief Investment Officer Ryan Israel said that the hedge fund bought Amazon shares at an "extremely attractive" price. He also expressed confidence that Amazon is able to handle any potential slowdown in its cloud business, Amazon Web Services.