Rocket Mortgage and Redfin are powerful brands and Dan Gilbert's company insists a streamlined process they plan to create would simplify homebuying.

The mortgage company Rocket is buying competitor Mr. Cooper in an all-stock deal valued at $9.4 billion, just weeks after acquiring real estate listing company Redfin.

Rocket Cos.’ $9.4 billion planned acquisition of loan servicer Mr. Cooper Group would put one in six U.S. mortgages under Rocket’s purview, according to the companies. That would create a mortgage behemoth.