Charlie Munger, who helped Warren Buffett build Berkshire Hathaway into an investment powerhouse, has died at a California hospital. He was 99.

Berkshire Hathaway said in a statement that Munger’s family told the company that he died Tuesday morning at the hospital just over a month before his 100th birthday.

“Berkshire Hathaway could not have been built to its present status without Charlie’s inspiration, wisdom and participation,” Buffett said in a statement. The famous investor also devoted part of his annual letter to Berkshire shareholders earlier this year to a tribute to Munger.

Munger served as Buffett’s sounding board on investments and business decisions and helped lead Berkshire for more than five decades and served as its longtime vice chairman.

Munger had been using a wheelchair to get around for several years but he had remained mentally sharp. That was on display while he fielded hours of questions at the annual meetings of Berkshire and the Daily Journal Corp. earlier this year, and in recent interviews on an investing podcast and also with The Wall Street Journal and CNBC.

Munger preferred to stay in the background and let Buffett be the face of Berkshire, and he often downplayed his contributions to the company’s remarkable success.

But Buffett always credited Munger with pushing him beyond his early value investing strategies to buy great businesses at good prices like See’s Candy.

“Charlie has taught me a lot about valuing businesses and about human nature,” Buffett said in 2008.

Buffett’s early successes were based on what he learned from former Columbia University professor Ben Graham. He would buy stock in companies that were selling cheaply for less than their assets were worth, and then, when the market price improved, sell the shares.

Munger and Buffett began buying Berkshire Hathaway shares in 1962 for $7 and $8 per share, and they took control of the New England textile mill in 1965. Over time, the two men reshaped Berkshire into the conglomerate it is today by using proceeds from its businesses to buy other companies like Geico insurance and BNSF railroad, while also maintaining a high-profile stock portfolio with major investments in Apple and Coca-Cola. The shares have grown to $546,869 Tuesday, and many investors became wealthy by holding onto the stock.

Munger gave an extended interview to CNBC earlier this month in preparation for his 100th birthday, and the business network showed clips from that Tuesday. In his characteristic self-deprecating manner, Munger summed up the secret to Berkshire’s success as avoiding mistakes and continuing to work well into his and Buffett’s 90s.

“We got a little less crazy than most people and a little less stupid than most people and that really helped us,” Munger said. He went into more detail about the reasons for Berkshire’s success in a special letter he wrote in 2014 to mark 50 years of helping lead the company.

During the entire time they worked together, Buffett and Munger lived more than 1,500 miles (2,400 kilometers) apart, but Buffett said he would call Munger in Los Angeles or Pasadena to consult on every major decision he made.

“He will be greatly missed by many, perhaps by nobody more than Mr. Buffett, who relied heavily on his wisdom and counsel. I was envious of their friendship. They challenged each other yet seemed to really enjoy being in each other’s company,” Edward Jones analyst Jim Shanahan said.

Berkshire will likely be OK without Munger, CFRA Research analyst Cathy Seifert said, but there’s no way to replace the role he played. After all, Munger may have been one of the few people in the world willing to tell Buffett he is wrong about something.

“The most pronounced impact, I think, is going to be over the next several years as we see Buffett navigate without him,” Seifert said.

Munger grew up in Omaha, Nebraska, about five blocks away from Buffett’s current home, but because Munger is seven years older the two men didn’t meet as children, even though both worked at the grocery store Buffett’s grandfather and uncle ran.

When the two men met in 1959 at an Omaha dinner party, Munger was practicing law in Southern California and Buffett was running an investment partnership in Omaha.

Buffett and Munger hit it off at that initial meeting and then kept in touch through frequent telephone calls and lengthy letters, according to the biography in the definitive book on Munger called “Poor Charlie’s Almanack: The Wit and Wisdom of Charles T. Munger.”

The two men shared investment ideas and occasionally bought into the same companies during the 1960s and ’70s. They became the two biggest shareholders in one of their common investments, trading stamp maker Blue Chip Stamp Co., and through that acquired See’s Candy, the Buffalo News and Wesco. Munger became Berkshire’s vice chairman in 1978, and chairman and president of Wesco Financial in 1984.

Berkshire’s legions of devoted shareholders who regularly packed an Omaha arena to listen to the two men will remember the curmudgeonly quips Munger offered while answering questions alongside Buffett at the annual meetings.

Munger was known for repeating “I have nothing to add” after many of Buffett’s expansive answers at the Berkshire meetings. But Munger also often offered sharp answers that cut straight to the heart of an issue, such as the advice he offered in 2012 on spotting a good investment.

“If it’s got a really high commission on it, don’t bother looking at it,” he said.

Investor Whitney Tilson has attended the past 26 years of Berkshire Hathaway annual meetings for the chance to learn from Munger and Buffett, who doled out life lessons along with investing tips. Tilson said Munger advised that after achieving some success “your whole approach to life should be how not to screw it up, how not to lose what you’ve got” because reputation and integrity are the most valuable assets, and both can be lost in a heartbeat.

“In the investment world, it’s the same thing is in your personal world, which is your main goal should be avoiding the catastrophic mistakes that could destroy an investment record, that can destroy a life,” Tilson said.

Munger famously summed that advice up humorously by saying, “All I want to know is where I’m going to die so (that) I never go there.”

Munger was known as a voracious reader and a student of human behavior. He employed a variety of different models borrowed from disciplines like psychology, physics and mathematics to evaluate potential investments.

Munger studied mathematics at the University of Michigan in the 1940s, but dropped out of college to serve as a meteorologist in the Army Air Corps during World War II.

Then he went on to earn a law degree from Harvard University in 1948 even though he hadn’t finished a bachelor’s degree. He co-founded a law firm in Los Angeles that still bears his name, but decided before long that he preferred investing.

Munger built a fortune worth more than $2 billion at one point and earned a spot on the list of the richest Americans. Munger’s wealth decreased over time as he gave more of his fortune away, but the ever increasing value of Berkshire’s stock kept him wealthy.

Munger has given significant gifts to Harvard-Westlake, Stanford University Law School, the University of Michigan and the Huntington Library as well as other charities. He also gave a significant portion of his Berkshire stock to his eight children after his wife died in 2010.

Munger also served on the boards of Good Samaritan Hospital and the private Harvard-Westlake School in Los Angeles. And Munger served on the board of Costco Wholesale Corp. and for years as chairman of the Daily Journal Corp.