If you'll notice, the Star Wars films have a very unorthodox construction. No opening credits at any point whatsoever. This was the superficial problem, but a big reason the DGA raised a stink was because Lucas refused studio funding after ANH, because then he'd have to kowtow to the whims of the director's guild and all the other trappings that come with signing for funding from a major film company.
After ANH, 20th Century Fox just did distribution of the film and got a good bit of the profit so they did marketing also. Lucas's real cash cow is the merchandise (duh).
That would be Bossk.