MATE RIMAC guides the Concept One—a prototype electric sports car he first designed when he was 21 years old—onto a stretch of road in Sveta Nedelja, a suburb west of Zagreb. The cherry-red vehicle is low, sleek and hardly subtle. Stepping gently on the accelerator, Rimac propels the car to 60 mph in less than three seconds. Jerking the steering wheel, he screeches through a roundabout before returning us to the parking lot outside Rimac Automobili—the Croatian engineer's automotive start-up—where he flings the car into a tight circle, pinning me hard against my seat.

"I'm...