If you memorize this phone number...
...then you will know the exact speed of light, in meters per second. :-D
Who discovered this? This lecture series by Prof. Michael Fowler from the University of Virginia's physics department has a wonderful condensed history on the subject.
There is also a whole ton of information on Wikipedia as well. Just like most things in science, the subject actually opens into a branching web of thoughts that probably touches on every other facet of human technical understanding. Why not start your journey with C? (the speed of light in a vacuum)