EKS was formed by Mattias Ekström, who is also a factory Audi DTM driver with a couple of championships under his belt in that series. He's been competing in various rally and touring car series for years, and even snagged a ride in a NASCAR Sprint Cup race back in 2010 at Infineon Raceway. The EKS team came together in 2014, with Ekström fielding an Audi S1 EKS RX Quattro. And the team hasn't done too badly for itself; in 2016, it took the driver's and team championships.
There's only so much Ekström's team as privateers can do to protect its championship from factory-backed teams, so that explains why Audi Sport was happy to step in with full support – including vehicle development supported by the actual motorsport department at Audi. Ekström will also continue on as a factory Audi DTM driver.