David L. Sokol, an executive at Berkshire Hathaway and deputy to Warren E. Buffett, resigned from his position in March 2011 after reports emerged that he had made a profit by buying the stock of a company in his own account shortly before Mr. Buffett announced he was buying the company.

Days after initiating merger discussions with Lubrizol, a specialty chemicals manufacturer, on Berkshire’s behalf, Mr. Sokol bought $10 million worth of Lubrizol stock, a position that increased by $3 million when the deal was announced in March.

In January 2011 meeting, Mr. Sokol approached Mr. Buffett about possibly buying the company. He made a brief admission to his boss: he owned stock in the takeover target though it led to no follow-up.

Mr. Sokol said he did nothing wrong, but on April 27 Berkshire Hathaway said that its audit committee had determined that he had violated the company’s standards of ethics in buying the shares of Lubrizol. The company directors accused him in April 2011 of misleading the company about his personal stake in the chemicals company.

Mr. Sokol never told Mr. Buffett that he had bought his stake in Lubrizol after Citigroup bankers had pitched the company as a potential takeover target, according to a report by the audit committee of the Berkshire board that was released in April.

The Securities and Exchange Commission is now investigating Mr. Sokol's trading. Mr. Buffett, who had been criticized for praising Mr. Sokol in the release announcing his departure, said that he had referred the matter to the head of enforcement at the S.E.C.

Confidential Information

In the press release, Mr. Buffet had declared that he did not believe the purchases “were in any way unlawful.” But securities lawyers say that regulators could argue that Mr. Sokol’s knowledge about Lubrizol was confidential information not only under Berkshire’s policy, but also under federal law.

Mr. Sokol has several potential defenses. Even though he bought Lubrizol stock, the possibility of a Berkshire acquisition was remote, it could be argued.

His sudden downfall came as a surprise to outsiders who had watched Mr. Sokol rise in the business world. He helped build a small Omaha energy business into a multibillion-dollar corporation, sold it to Berkshire Hathaway and by all appearances became one of his boss’s favorite executives. Mr. Sokol served as Mr. Buffett’s Mr. Fix-it, a turnaround artist trusted to tackle difficult jobs.

Entering Berkshire's Inner Circle

In some ways, Mr. Buffett and Mr. Sokol seem to share many similarities, suggesting an easy familiarity.

They were both born and raised in Omaha, Neb., and still reside there. Each man credits their early jobs as newspaper delivery boys and grocery store clerks, with instilling a strong work ethic. Their business writings are filled with homespun aphorisms.

It was his Omaha connections that helped Mr. Sokol pierce the Berkshire inner circle.

After earning an engineering degree in 1978 from the University of Nebraska at Omaha and working at a small firm, Mr. Sokol moved to a conglomerate called the Ogden Corporation. He took charge of a unit that developed waste-to-energy technology. At 32, he was chief executive of public company after a stock offering.

While at Ogden, he caught the eye of Walter Scott Jr., a man who would change his life. Mr. Scott was a childhood friend of Mr. Buffett, a member of the Berkshire board and chief executive of Peter Kiewit Sons, a construction company in Omaha.

In 1991, Mr. Sokol moved to Kiewit to acquire energy businesses. Mr. Sokol rapidly built the unit into MidAmerican Energy Holdings, and Berkshire in turn bought the company for about $9 billion in October 1999. It became one of Berkshire’s fastest growing and most profitable units, earning $1.2 billion in 2010.

Mr. Sokol’s personal wealth grew quickly, too. In his last three years as chief executive, a job he relinquished around 2007, his cash compensation topped $21 million. In 2009, he cashed in options on MidAmerican stock worth $96 million.

Mr. Sokol’s largest fix-it job became NetJets, which he took over in August 2009. Mr. Buffett praised Mr. Sokol’s restructuring and cost-cutting at NetJets in his annual letter in February 2011. “I can’t overstate the breadth and importance of Dave Sokol’s achievements,” he wrote, explaining that NetJets earned $207 million in 2010, a swing of $918 million from a big loss the previous year.

Management Style

But people who worked for Mr. Sokol saw a side of him that Mr. Buffett perhaps did not. His brass-knuckled approach alienated some Berkshire employees, as when he suggested that people with an illness or other personal problems were problematic and when he unceremoniously fired a top executive and made him leave the office that day.

Flashes of his management style can be found in some earlier litigation as well. In one civil case, a judge rebuked Mr. Sokol for tampering with his company’s numbers so that a joint-venture partner would get a smaller payout. In another case, Mr. Sokol sued to find out which employees at a Berkshire unit were disparaging him.

Mr. Sokol’s former employees say they are befuddled that someone who extolled the importance of ethics and integrity would find himself in such controversy.

In his self-published book, “Pleased, But Not Satisfied,” Mr. Sokol includes integrity as one of his business commandments.

“If you are uncertain about an issue,” wrote Mr. Sokol, quoting Mr. Buffett, “it’s useful to ask yourself, ‘Would I be absolutely comfortable for my actions to be disclosed on the front page of my hometown newspaper?’ ”

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