OMAHA, NEB. – Warren Buffett is called an oracle and a cult hero not just because he’s made himself one of the world’s richest people, but because he comes across as folksy and, above all, honest.

Now, he’s in the unusual position of having to explain a top Berkshire Hathaway executive’s questionable behavior.

The situation: A key executive thought to be a potential successor to the 80-year-old Buffett persuaded Buffett to buy a chemicals company that the executive had personally invested in. The executive, David Sokol, saw his investment grow by $3 million, or 29 percent, after Berkshire bought the company, Lubrizol.

Berkshire announced Sokol’s resignation late Wednesday.

On Thursday, the company’s stock fell 2.1 percent as investors worried whether the incident would tarnish Berkshire’s sterling reputation or become a distraction for the company.

Sokol’s actions may not have been illegal, experts say, but are still likely to attract the attention of investigators. And for a company that has carefully cultivated a squeaky clean reputation, it is a rare black mark.

“For a company that prides itself so much on its reputation for integrity, you can’t do stuff that doesn’t look right,” said Meyer Shields, an analyst at Stifel Nicolaus.

Both Buffett and Sokol have said the transaction had nothing to do with Sokol’s resignation. But in an unusual two-page letter announcing the resignation, Buffett laid out a timeline of events that suggests Sokol used his influence in Berkshire to recommend a deal that would benefit him personally.

It was the third time Sokol tried to resign in recent years. The other times Buffett convinced him not to. This time, Buffett didn’t even try.

Sokol’s sudden resignation raised alarms for investors because Sokol was seen as one of four possible successors to Buffett. While it is unclear if Sokol was indeed a candidate given his earlier resignation attempts, the issue of succession at Berkshire has long been a nagging concern for investors.

Sokol said in an interview with CNBC on Thursday that he has not been contacted by investigators and that he had done nothing wrong.

Buffett declined Wednesday and Thursday to answer questions about Sokol’s resignation beyond what he said in his statement.

Jacob Frenkel, a former SEC enforcement lawyer now at the firm Shulman Rogers in Rockville, Md., says Sokol’s actions likely do not constitute insider trading. Because Berkshire hadn’t made an offer to buy Lubrizol at the time Sokol bought shares, it appears Sokol wasn’t using significant confidential information — the definition of illegal insider trading.

Sokol bought 96,000 shares in Lubrizol Corp., a maker of specialty chemicals, at $104 per share about a week before he suggested to Buffett that Berkshire buy Lubrizol. Sokol told Buffett that he owned shares in Lubrizol, but he did not tell him when those shares were purchased.