Finished reading the book George Lucas: A Life this past weekend. It's a great read and offers a ton of insight into the building of the ILM and LucasFilm empire. Also some good tidbits in there if you like behind the scenes type of stuff as far as the production of movies go.
I found it interesting that his "brand" ILM, Skywalker Ranch, and LucasFilm happened mainly due to the fact that he was so damn stubborn. Don't get me wrong, he was pretty ballsy and took some big risks with the first Star Wars but his empire was created out of a need to do things his way in large part because everything else was seen as an inconvenience to him.
The book also puts to rest a lot of thoughts that people have about the OT. No, it was not all planned out from the beginning, IE: the overall story arc, and it was very much a fly by the seat of your pants thing. It wasn't until late in the production of ESB that the saga really changed and began to take shape as a family affair.
Spielberg made $40mil off of the franchise due to a bet with Lucas. He thought Star Wars would be huge and even bet Lucas 2.5% profit points that it would be bigger than Close Encounters. Lucas agreed and over the next 30years Spielberg would make $40mil due to that bet.