DuracellEnergizer said:

I wonder if Jabba was inspired by Baron Harkonnen from Dune. Both are morbidly obese to the point where they (initially) can't move on their own power and both have sexual tastes which are, for lack of a better description, less than mainstream.

The Declan Mulholland Jabba may have been--albeit with a large dash of Sydney Greenstreet added in. But slug-Jabba I think draws much more directly from Leto II in his sandworm form from God Emperor of Dune, which came out in 1981--right when Lucas began to write ROTJ.