thx1138 was george lucas's first film (commerically). That code THX 1138 has become something of an in-joke. Most of lucas's later film, star wars, indiana jones series had some drop-ins of THX-1138 (german war plane in indy film, and here and there in Star wars i forgot where have to watch all over again lol)
But more interestingly, it all started of when Lucas had to figure out a futuristic 'name' for the sci-fi which he was making in the film back in 1971 (or a bit before that, it waw released in 1971 for sure). So as it happened he named the film after his San Francisco telephone number, 849-1138 -- the letters THX correspond to letters found on the buttons 8, 4 and 9.
wierd way to call a film eh?
btw glad you put this thx-1138 for that number i wouldn have done the same, its a classic! really good film not for everyone, abit unrefined in some places, but i liked the story, it really get to show what society is capable of heading into if we dont watch it.