Warren Buffett said on Tuesday that he had donated about $866 million in Berkshire Hathaway stock to four family charities, telling shareholders "I'm 93 and feeling great, but I'm fully aware that I'm playing overtime," marking the end of the investor's storied investing career.

Berkshire said in a regulatory filing that Buffett donated 1.5 million Berkshire Class B shares to the Susan Thompson Buffett Foundation, an organization named after his late first wife that works in the field of reproductive health.

At the same time, Buffett also donated an additional 900,000 Class B shares, which were equally distributed to charities run by his children Howard, Susan and Peter: The Howard G. Buffett Foundation, Sherwood Foundation and NoVo Foundation.

It is worth mentioning that this time last year, Buffett donated $759 million worth of Berkshire shares to the above-mentioned charities.

Since 2006, he has donated more than half of his Berkshire stock to family charities and the Bill & Melinda Gates Foundation. These donations totaled nearly $52 billion at the time, of which the Bill & Melinda Gates Foundation received more than $39 billion.

In addition, Buffett also issued a rare letter to shareholders, insisting that more than 99% of his wealth will be donated to charity after his death, and that Berkshire itself will be under good management.

It is understood that Berkshire owns a series of mature businesses, including BNSF railroad, Geico auto insurance, energy and industrial companies, dozens of enterprises, as well as well-known consumer brands like Dairy Queen and Fruit of the Loom.

At the same time, the company also owns hundreds of billions of dollars worth of stock, led by Apple (AAPL). Shares of the conglomerate have gained nearly 17% this year after reaching an all-time high in September.

Berkshire's longevity

In the letter, Buffett confirmed to Berkshire shareholders that the business empire he has cultivated over the past six decades will stand the test of time even without his oversight.

"In the short term, Berkshire's unique characteristics and behavior will be supported by my large Berkshire holdings. However, before long, Berkshire will earn the reputation it then deserves," Buffett said. "Large institutions of all types, whether governmental, philanthropic or profit-seeking, can decline, but they are not inevitable. Berkshire's advantage is that it is built to endure."

It is reported that although Buffett has been reducing his responsibilities outside Berkshire over the years, he has never publicly expressed his intention to step down, including after being diagnosed with prostate cancer in 2012.

Greg Abel, Berkshire's vice chairman of non-insurance businesses, was named Buffett's successor.As CEO, Howard Buffett will serve as non-executive chairman. In this regard, Buffett praised Abel, pointing out that he shouldered most of the responsibility.

In addition, Buffett's three children are the executors of his will and the designated trustees of a charitable trust that will receive nearly all of Buffett's wealth. According to Forbes magazine, Buffett is the fifth richest person in the world, with a fortune of $120.5 billion.

"My children and I share the view that while dynastic wealth is legal and common in many parts of the world, including the United States, it is not desirable," Buffett said. "We have had many opportunities to observe that having money does not make you smart or evil."