Libya is rich in oil. Very much so.
And Gaddafi, despite having supported the western effort against Al-Kaida, is a solid old thug.
He has been bombed by the Brits before, and after that he behaved a bit better (well not always)
His old sins that are known, are the Lockerbie incident, assassination of a young Police officer in London (a Woman) which revealed that the Libyan embassy was an effective arsenal!, and launching missiles at Italy.
In 1989 2 Tomcats from USS JFK had a fight with Libyan Mig-23's.
There are many other incidents, - the bottom line is that the guy is trouble.