He's bought one of those stocks in each of the past four quarters, amounting to $7.1 billion in total during that period. And while the stock is up significantly since this time last year, there's still a good chance he's buying more this month.

Warren Buffett bought his first shares of stock at age 11 back in 1941. Over the next 83 years, the "Oracle of Omaha" has used his value investing prowess to amass a fortune worth about $138 billion, even after donating more than $56 billion to charity.

Since that initial position, Berkshire has continued to acquire more shares. Today, its stake has nearly tripled, to about 250 million shares worth roughly $15 billion. More than four million of those shares were purchased in the last quarter alone. Berkshire still holds most of its warrants, too, which are now in the money.