The longest serving head of state currently is President Omar Bongo of Gabon, serving since November 28, 1967. Gaddafi has been in power since September 8, 1969.
Why have I never heard of this guy? Bongo, that is.
I'd never heard of him either. I guess it's because Gabon is not an important country.
I guess, but still...
Just read his
Wikipedia article - while it seems he might be a bit corrupt, (which one would probably expect from someone who's been in power that long) it doesn't appear he's done anything outright tyrannical or otherwise outrageous. Combined with the low profile of his country in terms of international recognition it's little surprise you, myself, and others haven't heard of him.