Fans of some of James Cameron's films can be a bit, um, rabid. Titanic was such a hit that its romantic theme song has been harassing wedding guests ever since. Avatar fans have attempted to perfect their lucid dreaming in order to transport themselves to Pandora. They have even learned the Na'vi language so they can mingle once they're there.
The Terminator may not enjoy the same level of—let's call it dedication, but the film and its subsequent franchise have managed to maintain a solid fandom for the past 30 years.
The film is a pop culture legend, with TV series like The Simpsons, Bob's Burgers, South Park, Family Guy, and Futurama reverently referencing it in various episodes. And those are just the animated shows. Arnold Schwarzenegger's entire acting career is basically a giant shout-out to his first hit. If you don't know the film, chances are hundreds of in-jokes have flown by you.
With a new film coming out every 7 years on average, the franchise has had to expand into other media to give the fans their drip feed of T-800 content. We're talking books, comics, and video games. Comics have taken particularly odd story routes that serve as a kind of pop culture battle royale. The illustrated panels have shown the Terminator battling everyone from RoboCop to Superman to aliens to Wolverine.
Perhaps the most famous example of franchise expansion is the story-driven ride at Universal Studios. Titled Terminator 2: 3-D, it combines "3-D cinematography, digital graphics, and live-action stunts" (source). It was directed by Cameron and even starred the cast from the second movie. The ride has been up for 20 years and is still going strong at Universal Studios' Orlando resort.
Of course, the fans themselves have kept the franchise alive. Can you imagine a convention without a Terminator cosplayer? Or the internet without a petition to resurrect The Sarah Connor Chronicles? And let's not forget the fanfiction. A cohort of Russian novelists couldn't produce enough pages to match.