(Reuters) - Ajit Jain, the longtime top insurance executive at Warren Buffett's Berkshire Hathaway ( BRK/A ), sold more than half of his Class A shares in the conglomerate this week.

According to a Wednesday night regulatory filing, the 73-year-old Jain sold 200 Berkshire Class A shares on Sept. 9 for about $139.1 million, at an average price of $695,418 per share.

The sale included 104 shares Jain held directly and 96 held by family trusts. No reason was given for the sale.

Berkshire did not immediately respond on Thursday to a request for comment.

Jain's selling occurred five days after Berkshire's share price peaked above $727,000, and less than two weeks after its market valuation topped $1 trillion for the first time.

Berkshire has slowed its own stock repurchases and let cash build to a record $277 billion.

Cathy Seifert, an analyst at CFRA Research who rates Berkshire a "buy," said Jain's selling may reflect personal circumstances rather than his view of Berkshire's prospects.

"Those of us who have watched Berkshire Hathaway ( BRK/A ) for a long time have suspected there may be a changing of the guard in insurance operations," she said. "My sense is that he may be moving on, and I suspect that is behind his stock sales."

Jain still oversees 166 Class A shares, including 61 held directly and 105 held by the trusts and his nonprofit Jain Foundation.

He also oversees 124,308 Berkshire Class B shares, equal to about 83 Class A shares, held by the foundation.

Born in India, Jain joined Omaha, Nebraska-based Berkshire in 1986 and led its expansion in reinsurance, with a specialty in pricing for large risks such as natural catastrophes.

Buffett has credited Jain with adding tens of billions of dollars of shareholder value, and once said that if he, Jain, and late vice chairman Charlie Munger were in a sinking boat and only one could be saved, "Swim to Ajit."

Greg Abel, 62, Berkshire's other vice chairman, is expected to eventually succeed Buffett, 94, as chief executive.