Jeff Jones was a fantasy illustrator who was mostly popular in the 1970's. Frank Frazetta has been quoted, saying that Jeff Jones is "the greatest living painter." Jones' website is extremely bad, but if you have the patience you can find some really cool stuff on it here. Also a gallery of all of Jones' paperback covers can be found on Vintage Pbks here. I found a really interesting, recent interview with Jones over at Sequential Tart here.