Farris Wilks and his younger brother Dan are billionaires thanks to the recent oil-and-gas drilling boom. They’re also the biggest donors in the 2016 race for the White House, giving $15 million to a Super PAC backing Republican presidential contender Ted Cruz.

A Reuters investigation published today finds that the largely unknown Wilks family has outspent the billionaire Koch brothers, Charles and David, who have pledged to use their Freedom Partners network of conservative donors to pour $1 billion into the campaign.

Some other key facts about the Wilks brothers: