Dan Aykroyd, Harold Ramis, and Ivan Reitman
It all started with SNL veteran Dan Aykroyd's secret (or not so secret) obsession with ghosts. Aykroyd came by his spectral fixation honestly. In a Vanity Fair article, he's quoted as saying, "It's the family business for God's sake" (source). Turns out his great-granddad was actually a renowned spiritualist, and the Aykroyd family farmhouse in Ontario used to be the scene of tons of séances (!).
On top of that, his grandfather researched ways to communicate with ghosts via radio technology, and his dad wrote a history of ghosts. So it might've seemed out of left field to some when Aykroyd came up with the idea of making a comedy about some dudes who bust ghosts, but to Aykroyd it was a no-brainer.
Aykroyd's first draft of the script was way different than the version of Ghostbusters that we know and love. The original vision was more out there with the Ghostmashers, as they were called, traveling through different dimensions to bust (er, mash) tons of gargantuan ghosts (including the Stay Puft Marshmallow Man).
However, Aykroyd's dimension-hopping dream got squashed after he pitched the script to big time comedy producer/director Ivan Reitman. It took Reitman like two seconds to say, "Danny, baby. It's a fab idea, but it's going break the bank." (That's how producers talk, right?) Reitman then pitched some massive changes to Aykroyd, which totally redefined the movie, like when he said "Danny, baby. What if it's set in NYC?" and "What if they go into business? It's the 80's; everybody and their mother is going into business."
(Again: we have no idea if Ivan Reitman actually talks like this.)
Ramis Has Entered the Building
To help Aykroyd bring his script down to Earth, Reitman drafted Harold Ramis, who'd written a slew of top-shelf comedies at this point, including Animal House, Caddyshack, Stripes, and Meatballs.
After that, Aykroyd, Ramis, and Reitman hunkered down in a bunker on Martha's Vineyard and hammered out a drastically different version of the script in about two weeks. Ramis is quoted as saying "Dan's great at creating funny situations, whereas my strength is more in the area of strong jokes and funny dialogue. Essentially, we wrote separately, and then rewrote each other" (source).
Whoever did whatever, the script that emerged from that bunker turned out to be what many call the best comedy of the '80s. Who knew a bunker was the place to go to find that creative spark?
And who knew Martha's Vineyard had bunkers?
The Lovecraft Connection
Okay, time for a quick tangent. Don't mind us.
As we noted earlier, Dan Aykroyd actually had a lot of knowledge about the supernatural, which he drew upon to put the film's weird mythology together. But he also drew upon a fiction writer when creating Gozer, Zuul, and the general nuttiness going on in Dana Barrett's apartment. HP Lovecraft, considered second only to Edgar Allan Poe among American horror authors, provided a template on which they could create these demonic gods.
Lovecraft's stories often revolved around creatures older than time that dwelt in outer space or other planes of existence. The universe actually followed their rules of morality, not ours. We were an anomaly and, sooner or later, they were going to show up and wipe us all out. Lovecraft wrote about characters stumbling onto this disturbing truth, and usually going mad as a result.
Ghostbusters wasn't willing to go quite that dark, but they drew on some of Lovecraft's seasoning to make the threat of Gozer real. So, we get Egon's speech about the weird composition of Ms. Barrett's building and the creepy cult that used to operate there. When Gozer arrives, it quickly gets put into a ridiculous shape (we love you Mr. Stay Puft), but the threat is still there, and Gozer isn't talking about just knocking over a few buildings. If our boys don't step up, the whole human race is going to come to a gooey, sugar-coated end…and if you look past the sheer ridiculousness of it all, you can spot Lovecraft, winking merrily at us.