The cantina sequence was, along with the dogfights between the starfighters at the end of the movie, one of the sequences that George Lucas came up with at the beginning of his conception for "Star Wars." No matter how often the story changed in various drafts, the cantina sequence remained.
Filming began on Tuesday, April 13, 1976. The cantina was populated by 42 extras portraying a bunch of humans, humans with prosthetic pieces making them "ugly humans" and various aliens put togther by make-up artist Stuart Freeborn (seen here with Peter Mayhew as Chewbacca) with the aid of his family and assistants. The creatures were created based on costume designer John Mollo's sketches.
Because the cantina sequence kept getting bumped forward on the shooting schedule, and because Freeborn ended up getting sick and was unable to finish all of the creatures in time, only the creatures meant to be background aliens were finished in time. None of the key monsters were completed. Essentially, what you see in all of the master shots of the cantina, where the bar itself is in shot, were all of Freeborn's background creations. A lot of them were also used on the streets of Mos Eisley as background extras as well, as seen in the black and whitegroup shot shown below.
Not only did Lucas decide the sequnce needed beefing up, but a number of elements originally filmed ended up being cut, including footage of Han Solo making out with girlfriend, Jenny, in his booth before Ben, Luke and Chewie come to join him.
Insert shots would be filmed in Los Angeles on January 24 and 25, 1977 to spruce up the sparse looking population of the cantina and to really elevate the bizarre quality of the scene that Lucas wanted from the beginning.
Working from sketches primarilly by Ron Cobb, make-up artist, Rick Baker supervised a team of stop-motion animators who sculpted, painted, and usually ended up wearing the alien masks that were created to fill out the scene. From left to right in the crew photo (with the masks on a table) below, are Laine Liska, Phil Tippett, Jon Berg, Doug Beswick, and Rick Baker. Not shown is Rick Baker's assitant, Rob Bottin, who was not even 16-years old at the time, and who would later go on to do the make-up effects for "The Howling" and John Carpenter's "The Thing."
All of these insert shots, essentially used for cut away reaction shots, as well os isolated alien interactions when Luke looks around the cantina upon first entering it, were filmed in the same alcove; the only part of the cantina set recreated for the insert shots. Footage of Greedo was reshot, using a modified mask that was capable of movement. In England, for the master shots, it was worn by Paul Blake. In the American inserts it was worn by Maria de Aragon. In the image accompanying the article below, it appears that Greedo's hands were replaced with gloves created for one of the Duros aliens.
To supplement the masks specifically created for the inserts, Rick Baker added a bunch of masks he'd created previously, that hadn't been used in prior productions. Here, I've included a shot of Rick Baker (with then wife, Elaine) wearing the mask that would become known as the Stennes Shifter, as well as an image of Baker in his demon costume which was created with a bat-like mask over the bodysuit he created for the title character of John Landis' "Shlock," combined with the hands of the mutant baby for "It's Alive." This costume was used for the demon in a live staging (see image filled with smoke) of a show based loosely on "The Exorcist" put together for one of Bob Burns' legendary Halloween shows. (For more on these, come back in October). The devil-like mask for the Devaronian, Labria was also a pre-existing Baker mask, as was the wolfman mask used for Lak Sivrak (since replaced in the so-called "special edition".
As a bonus, here is the complete article by Paul Mandell on the cantina inserts that was featured in Cinefantastique magazine double issue Vol6No7/Vol7/No1 from Spring 1978.