Erin Catto is your typical programmer: he loves math and physics. So much so that, six years ago now, he wrote and freely distributed a physics engine for video games called Box 2D. It was simple. It was effective. It was small.

And it’s the primary physics engine for “Angry Birds,” turning Rovio into a billion-dollar company and rewarding Catto with…a sweatshirt he doesn’t even wear:

“I have the sweatshirt but actually I have never worn it because it’s red”, he told NPR. “I generally don’t wear red. That’s a silly reason. If they would send me a blue one I would wear it!”

Catto isn’t particularly bothered by the fact that something he wrote made some other company a huge success: Box 2D was so amazing he easily landed a high paying job at another digital crack dealer, namely Blizzard, as a Principal Software Engineer. And he’s just happy people like his code.

But, seriously, Rovio, at least send him a blue sweatshirt. And maybe buy him a house. You owe him.

(Image via Rovio)