Possibly no other movie has contained as many pop cultural references as “Monsters vs. Aliens.”

Co-director Conrad Vernon said that from the start, the film was conceived as a cheeky homage to classic monster and sci-fi films.

“It was a great idea … plus they gave me a budget to buy as many old horror films as I wanted. So I bought about 150 DVDs of films from the early ’50s and ’60s, and everybody on the project got to see them.”

Vernon means everybody.

“People from the art department, the effects department, the story department – everybody got to check out these movies and draw from them. So we had ideas coming in from everybody, not just story people or artists but from lighting people, the executives. Everyone was pitching ideas to be included in the movie.”

The final film is so crammed with homages to old movies that you’d have to watch it several times to catch them all – and even then you’d miss some.

In a recent telephone call Vernon, whose credits include “Shrek 2,” offered some insights into the film’s characters and situations and the old movies that inspired them:

Susan Murphy/Ginormica (voiced by Reese Witherspoon): “Everyone thinks of ‘Attack of the 50 Foot Woman,”‘ Vernon said. “Which is true, but we wanted to make sure we weren’t basing our characters on just one movie. We were exploring subgenres: mad scientists, oozing gooey characters, mutants that are half this and half that … and, of course, the whole giant human genre.”

B.O.B. (Seth Rogen): B.O.B. is a gelatinous blue globule with one big eye. He’s an obvious reference to the 1958 Steve McQueen movie “The Blob.”

“I saw ‘The Blob’ when I was a little kid,” Vernon recalled. “My baby sitter and I sat up to 2 a.m. watching. It was great. There was this oozy character that whenever it touched you sucked all the moisture out of you.

“Of course, B.O.B. doesn’t hurt people, but he sometimes inadvertently sucks them in.”

The Missing Link (Will Arnett): “There’s a lot of the ‘Creature from the Black Lagoon’ there,” Vernon said, “but also some ‘King Kong’ and some ‘Piranha’…there’s just a whole bunch of influences.”

Insectasaurus : This one’s too easy – at least for anyone who’s ever seen the Japanese character Mothra, the skyscraper-sized bug who tore up Tokyo in a 1961 release.

Dr. Cockroach (Hugh Laurie): A fellow with a human body and the head of an insect, he’s an obvious nod to 1958’s “The Fly.” His laboratory apparatus is modeled after the one in the 1986 “Fly” remake.

Gen. W.R. Monger (Kiefer Sutherland): Monger runs a top-secret federal prison for monsters.

Says Vernon: “We were thinking of ‘Dr, Strangelove’s’ Buck Turgidson” – portrayed by George C. Scott – “when we started out. But when we cast Kiefer we didn’t tell him that this was based on the ‘Strangelove’ character. We simply explained that Monger was a grizzled WWII vet who has spent 50 years capturing and controlling these monsters.

“Kiefer envisioned him as the drill sergeant from ‘Full Metal Jacket’ mixed with the cartoon character Yosemite Sam. So there’s a little bit of all those people in it, filtered though Kiefer’s sensibility.”

“Monsters vs. Aliens” also has a scene set in the Pentagon’s War Room that’s a dead ringer for the one in “Strangelove.”

“My co-director Rob Letterman and I are huge Stanley Kubrick fans, and that’s one of our favorite movies. Thanks to that film you think of the War Room as a big cavernous place with a big board and all these people working at terminals like an air traffic control center. But I’ve seen photos of the real War Room. It’s like a conference room with chairs and a few TVs. Very disappointing.”

Gallaxhar (Rainn Wilson): A megalomaniac from another planet, Gallaxhar has arrived to colonize earth with an army of killer robots.

“Designing Gallaxhar we asked ourselves what were the most common design traits of ’50s sci-fi monsters,” Vernon explained. “We came up with big bulging brains, slimy tentacles, multiple eyes and a costume made of some sort of Lycra or satiny material.”