Robert Mercer, a New York hedge fund billionaire, and his middle daughter, Rebekah, have been the secret force behind the new Donald Trump staffing appointments and other decisions being made by the GOP presidential nominee. The mega-donor family duo orginially funded a Super PAC to aid Ted Cruz, but have since turned their attention to aiding Trump defeat Hillary Clinton.

Rebekah, a Heritage Foundation trustee and director of the Mercer Family Foundation, leads the operations of the Mercers’ political agendas, while her father Robert provides the funds and means to monetarily thrive against Democratic nominee, such as the creation of the Defeat Crooked Hillary PAC.

The Mercers were in fact furious when Cruz didn’t endorse Trump at the Republican National Convention last month. Regardless, the Mercers are united in their deep opposition to Clinton, and have been constantly working behind the scenes in Trump’s favor. They worked with newly appointed Steve Bannon and provided funds for the “Clinton Cash” movie, based on the book by Peter Schweizer.

Little has been written about the Mercers because they avoid the public spotlight and relish in their anonymity, but conservative sources who know the family describe them as “kind, civic-minded people and consensus-builders.” How much influence they actually hold on Trump, considering his anti-establishment and anti-corruption stance, is still debatable.