Warren Buffett has made some rather bearish moves in Berkshire Hathaway's (NYSE: BRK.A)(NYSE: BRK.B) stock portfolio in the past few quarters. Most notably, the legendary investor disposed of significant portions of both the Apple and Bank of America investments that have performed extremely well for Berkshire.

Steve Ballmer has an unorthodox investing approach. The former Microsoft CEO is worth $151 billion, per the Bloomberg Billionaires Index, making him the ninth richest person the world. That puts him ahead of famed investor Warren Buffett by a nearly $10 billion margin.

The purchases were made Tuesday through Thursday. The Occidental Petroleum buy was the first since June, suggesting Berkshire CEO Warren Buffett now finds the stock attractive.

Since Warren Buffett became the CEO of Berkshire Hathaway ( BRK.A 0.80%) ( BRK.B 0.95%) in 1965, its stock has delivered a compound annual return of 19.8%. That would have been enough to turn a $1,000 investment into $42.5 million, whereas the same investment in the S&P 500 would have grown to just $325,053 over the same period.