Legendary US investor Warren Buffett -- in a 2011 letter to shareholders of his Berkshire Hathaway investment group -- famously compared the entire world's gold stock of 170,000 metric tons, valued at $9.6 trillion (pile A) with another set of assets costing an equal amount (pile B).
In the context of the input sentence, determine the relationship between 'Berkshire Hathaway' and 'Warren Buffett'.
Options: founded by, owned by, chief executive officer, legal form