“Star Wars” is full of fascinating, enigmatic villains, most of them get barely any dialogue, let alone their background or backstory explained — in the movies at least. Whether it’s Darth Vader being introduced as just a tall, menacing guy clad in dark, robotic armor, or Boba Fett’s silent, striking suit of armor, these antagonists work because of how little we know of them, and how memorable their designs are.

This is especially true in the prequel trilogy, where we get characters like Darth Maul, who is just evil incarnate, a perfect design. Though perhaps not as well-liked, General Grievous’ own character design is just as effective. He’s a villain who’s instantly memorable and striking, his cybernetic exterior and biological organs making him rather mysterious and alluring.

Grievous, like most things “Star Wars,” went through many changes before making his debut, with George Lucas even briefly considering making the character Darth Maul in disguise. The general was first introduced in the 2003 animated micro-series “Clone Wars” by Genndy Tartakovsky, where he was voiced by John DiMaggio and Richard McGonagle, before making his big screen debut in “Star Wars: Episode III — Revenge of the Sith.” In that film, Grievous was voiced by sound editor and voice actor Matthew Wood, who would go on to reprise the role in the cartoon series “The Clone Wars” (where he also voices the battle droids and many others).

But before Wood became the voice of Grievous, the asthmatic cybernetic villain was almost portrayed in “Revenge of the Sith” by none other than Oscar-winner Gary Oldman. Once, while appearing on the “Happy Sad Confused” podcast, Oldman said he even recorded some lines for the character, directed by Lucas himself. So what went wrong? According to Oldman, “What happened was something to do with union stuff and non-union stuff,” adding that he didn’t want to be “the poster boy for breaking union rules.”

The reason Oldman was unable to voice Grievous in “Revenge of the Sith” had to do with the film being a non-SAG shoot that took place in England and Australia — as all “Star Wars” movies have. There is a regulation within the Screen Actors Guild known as Global Rule One, which ensures members retain their full union protections even if they work abroad. Though Lucasfilm asked for special permission to have Oldman take part in a non-union production, the actor ended up having to take a pass on the film.

This is far from the first time George Lucas had difficulties with unions and guilds, with whom the director has had a long, uneasy, and complicated history. It started after the release of “Star Wars: Episode V — The Empire Strikes Back” in 1980, when Lucas very publicly left the Director’s Guild of America after a dispute regarding the use of an on-screen director credit. Though Lucas has received awards from the Producers Guild (of which he presumably is still a member), he is also not technically a member of the WGA. Instead, the retired filmmaker is a “fi-core member,” meaning he resigned his full membership to the writers’ union and instead pays his dues and union contract benefits, but otherwise does not have to follow any union rules, including union strikes.

In 1981, Lucas even became the very first person to become a fi-core member of the WGA — although the list soon came to include other notable filmmakers such as Francis Ford Coppola, Bob Gale, Robert Rodriguez, and Steven Soderbergh.