I've written about Jabba the Hutt previously, but never really in the context of Return of the Jedi and since he is such a large component in this movie, I thought I should revisit him.
As most everyone knows, Jabba's cinematic adventures began as a human actor in the first Star Wars movie who was meant to be replaced by a stop motion creature. this footage was never completed -- until it was revisited and altered for the Star Wars Special Edition in the 1990s so that Jabba became a CGI version of the slug-like creature we were familiar with from Return of the Jedi. Above is a storyboard frame depicting the actor portraying Jabba along with a superimposed creature version of him that would appear in the finished film. Despite being a bipedal creature, Jabba surprisingly doesn't look all that different from how he finally ended up looking in Return of the Jedi. Note also the lemur-like creature next to him, which corresponds with Jabba's pet/court jester, Salacious Crumb in Return of the Jedi. George Lucas was fond of lemurs and kept trying to work into the Star Wars movies an alien species that was based on them. This would finally happen in the Clone Wars television series.
Given how close the image of Jabba in the above storyboard would represent his final, approved look for Return of the Jedi, it's surprising that that storyboard image was not the starting point for Jabba's design, work that would be tackled by artists Ralph McQuarrie, Joe Johnston, Nilo Rodis-Jamero, and Phil Tippett who worked from George Lucas's instruction that Jabba have a sluglike body.
Nilo Rodis-Jamero thought of Jabba as being like a queen bee who is physically helpless, but is waited on and cared for, while exerting tremendous power over those in her hive. Jabba began to achieve his final look when Joe Johnston took Ralph McQuarrie's saggy fleshed heads and gave them a more cunning and sinister expression as shown below.
Stop motion animator took the drawings and sculpted a number of small maquettes including this one.
The schematic above shows how the enormous full size puppet of Jabba would be operated by a crew of puppeteers stashed within, without, and beneath Jabba's massive body.
Above are the operators (minus the little person who worked the tail) who provided Jabba with a wonderful, nuanced performance which must have required quite a bit of coordination on their part.