The world's biggest asset manager runs $4 trillion in investor assets — a sum so massive that it's bigger than the annual GDP of either France or Germany. It's nearly twice the size of the entire exchange-traded fund market globally ($2.22 trillion at last check).

And yet ETFs are growing fast enough that they are becoming the key engine of BlackRock's growth. The firm, which is also the world's biggest ETF company, just reported third-quarter results. ETFs accounted for 80% of BlackRock's $25.3 billion in long-term net inflows for the period. They're still a few percentage points shy of 25% of the company, as total assets go.