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.

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.

The financial technology platform Rocket Companies has acquired the Mr. Cooper Group mortgage company, which creates an entity that will represent nearly 20% of all mortgages in the United States.