It's the birthday of the man who finally perfected internal-combustion, Nikolaus Otto. While he was a travelling salesman he heard about the Lenoir internal-combustion engine, and started experimenting on his own.
After developing a carburetor for the Lenoir engine, which allowed the use of liquid fuel instead of the pain-in-the-ass to store and more gaseous fuel, he started to look at the engine's fundamental cycle, and found it lacking.
Internal combustion engines of the time roughly mimicked the steam engines that preceded them, in that they were using mostly atmospheric pressure in the cylinder to get things done. Otto added a compression stroke to really maximize the power of the combustion stroke, and in doing so, created the first viable four-stroke engine as we know it.
Now, Otto only ever made stationary engines, and the actual four-cycle concept with a compression stroke was actually first concieved 16 years earlier by Alphonse Beau de Rochas, but that guy never built any engines that used the principle, so Otto gets the props here.
So, Happy Birthday, Nick! I hope in whatever afterlife you're in you have access to something to see that embarrassing animated GIF I made of you because, you know we love you.
(Thanks for reminding me, jessethouin!)