Did some digging. It was Gary Kurtz, who quit after ESB.
From Wiki (And pretty much matches my remembrances of articles years gone) Kurtz has claimed that he and George Lucas clashed over how to progress the Star Wars series. Kurtz recalled after Raiders of the Lost Ark in 1981, Lucas became convinced that audiences no longer cared about the story; they were simply there for thrills and entertainment, and he began to deviate from the original nine-episode bible starting with Return of the Jedi, at which point Kurtz quit the series.
Re: George Lucas' leash
Did some digging. It was Gary Kurtz, who quit after ESB.
From Wiki (And pretty much matches my remembrances of articles years gone)
Kurtz has claimed that he and George Lucas clashed over how to progress the Star Wars series. Kurtz recalled after Raiders of the Lost Ark in 1981, Lucas became convinced that audiences no longer cared about the story; they were simply there for thrills and entertainment, and he began to deviate from the original nine-episode bible starting with Return of the Jedi, at which point Kurtz quit the series.