Analyze the relationship between 'Warren Buffett' and 'Berkshire Hathaway' within the context of the input sentence.
Options: employer, product/material produced, owner of, brand

It should come as no surprise that the most popular of these portfolios is that of renowned investor Warren Buffett , CEO of Berkshire Hathaway ( BRK.B ) and one of the richest people in the world.
owner of