PASADENA, Calif. — The two men who run Berkshire Hathaway Inc. have an arrangement: Warren Buffett is the face of the company and Charlie Munger stays mainly in the shadows.

That works well for the two billionaires, who together have developed one of the most successful investment records ever.

But while Munger downplays his own contributions — he is known for repeating "I have nothing to add" after Buffett's expansive comments at the Berkshire shareholder meetings — his role is key to much of the company's success.

Buffett himself credits Munger with pushing him beyond his early investing strategies and says the two men have never had an argument — even though they occasionally disagree.

Munger's influence as vice chairman of Berkshire is considerable, but mostly private.

"He strikes me as somebody who is just a very good sounding board for Warren," said Morningstar analyst Justin Fuller.

Berkshire's board has a plan in place to select a new management team for the time when Buffett and Munger are gone, but whoever takes over the company will have a hard time matching their success and synchronicity.

Munger answers questions alongside Buffett for hours each May at the Berkshire shareholders meeting in Omaha, Neb., and again on his own at the annual meeting in California of Wesco Financial Corp., a Berkshire subsidiary that he leads.

Buffett sometimes relies on Munger to repeat questions because his hearing is better. After one shareholder asked a lengthy question this year about how Buffett got started investing and what mindset an investor should have, Buffett turned to Munger for help.

So Munger summed it up: "He wants you to instruct him how to become less like a lemming."

When Munger does weigh in, he often cuts through Buffett's longer answer to its heart. And sometimes he critiques Buffett's response.

"Well, that was real useful advice," Munger said this year after Buffett answered a question about choosing good managers by saying Berkshire buys businesses with strong management teams in place. Then he compared that to saying the best way to get through lean times is to keep a couple million dollars lying around.

He can get away with rebuking the world's richest man because they've been friends for nearly 50 years.

Munger, who at 84 is seven years older than Buffett, grew up in Omaha about five blocks from Buffett's current home. Both men worked at the grocery store Buffett's grandfather and uncle ran.

By the time they met at an Omaha dinner party in 1959, Munger was practicing law in Southern California and Buffett was running an investment partnership in Omaha.

"We hit it off," Buffett said. "We were soon rolling on the floor laughing at our own jokes."

After that initial meeting, Buffett and Munger kept in touch through frequent telephone calls and lengthy letters, according to the biography in Munger's book "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.

Most of Munger's roughly $2 billion fortune comes from his 15,181 Class A Berkshire shares, which represent about 1.4 percent of the outstanding shares. The $100,000 salaries Munger and Buffett both receive from Berkshire haven't changed in more than 25 years.

Berkshire's book value — assets minus liabilities — per share has grown from $19 in 1965 to $78,008 now under their leadership — despite Munger and Buffett living more than 1,500 miles apart during the entire time they've worked together.

They organized Berkshire Hathaway so they wouldn't ever have much to do besides sit around and think. And that's still how they run the company today, even though it has grown to include roughly 250,000 employees and more than 70 subsidiaries.

"Neither Warren nor I is smart enough to make the decisions with no time to think," Munger said. "We make actual decisions very rapidly, but that's because we've spent so much time preparing ourselves by quietly sitting and reading and thinking."

The real key to Berkshire's success, Munger said, is that he and Buffett like learning and have improved over time. But Munger gives Buffett most of the credit.