You remember the blue blob. You definitely remember the giant lady. But honestly, if you sit down and look at the actual Monsters vs Aliens actors list today, it feels less like a 2009 animated flick and more like a fever dream of mid-2000s comedy royalty. It’s kinda wild. We’re talking about a cast that includes everyone from a future Ant-Man to the guy who played House.
Back when DreamWorks dropped this in March 2009, they weren't just making a movie; they were trying to prove that 3D wasn't a gimmick. They spent a fortune. But the real "secret sauce" wasn't the stereoscopic tech. It was the voices.
The Voices Behind the Chaos
Let’s talk about Susan Murphy, or Ginormica. Reese Witherspoon voiced her right at the height of her "America's Sweetheart" era. Susan is basically the heart of the movie, this normal woman who gets hit by a meteor on her wedding day and grows 50 feet tall. Reese actually turned down a bunch of other animated roles before this because she wanted a female lead that felt like a real superhero. She’s gone on record saying she loved that Susan wasn't just a sidekick.
Then there’s B.O.B.
Seriously, who else could play a brainless, gelatinous mass but Seth Rogen?
✨ Don't miss: Austin & Ally Maddie Ziegler Episode: What Really Happened in Homework & Hidden Talents
B.O.B. stands for Benzoate Ostylezene Bicarbonate (try saying that five times fast), and Rogen basically just leaned into his natural laugh. Most people don't realize B.O.B. was actually inspired by The Blob from 1958, but with way more personality and significantly less "eating everyone in town." Rogen’s improvisational style is all over those lines.
A Breakdown of the Monster Squad
It’s easy to forget just how stacked the rest of the lab was.
- Dr. Cockroach, Ph.D.: Played by Hugh Laurie. This was peak House era. To get him the role, an animator actually did a test of Laurie’s Emmy acceptance speech and put it over a cockroach. It worked perfectly. He’s the "mad scientist" of the group, and yes, he actually holds a Ph.D. in dance.
- The Missing Link: Will Arnett brought that gravelly, macho energy. He’s basically a prehistoric fish-man who thinks he’s way more athletic than he actually is.
- General W.R. Monger: You’ve got Kiefer Sutherland here, doing a voice that sounds nothing like Jack Bauer from 24. He’s the guy who has been running the secret prison for fifty years.
- Gallaxhar: The villain. Rainn Wilson (Dwight from The Office) played the four-eyed alien overlord. Interestingly, the character was originally supposed to be a woman, but they changed it because Madagascar 2 had just released a female villain and they didn't want to repeat the vibe.
The Weird Connections You Probably Missed
If you’re a fan of The Office, this movie is basically a reunion. You have Rainn Wilson (Dwight), John Krasinski (Jim), and Ed Helms (Andy) all in the same project. Krasinski and Renée Zellweger actually have these tiny cameos at the start of the movie as Cuthbert and Katie, the couple in the car who see the first alien robot land.
🔗 Read more: Kiss My Eyes and Lay Me to Sleep: The Dark Folklore of a Viral Lullaby
And then there's the President.
Stephen Colbert voices President Hathaway. He plays the keyboard to try and communicate with the aliens (the "Axel F" theme from Beverly Hills Cop). Fun fact: the character was designed before Colbert was even cast, but it ended up looking exactly like him anyway. It was a weird coincidence that everyone just rolled with.
Why the Casting Still Matters
People often write off animated movies as "just for kids," but the Monsters vs Aliens actors were playing characters that dealt with some pretty heavy themes—at least for a PG movie. Susan is dealing with gaslighting from her fiancé, Derek (voiced by Paul Rudd).
💡 You might also like: Kate Moss Family Guy: What Most People Get Wrong About That Cutaway
Derek is arguably the real villain. He’s a local news weatherman who cares more about his career in Fresno than his own fiancée. Rudd plays him with this perfect, smarmy "nice guy" energy that makes you want to see him get stepped on.
Production Secrets
- The movie took about 4.3 years to make.
- If you tried to render this whole movie on one computer, it would have taken 4,071 years.
- B.O.B. is technically a cross between a genetically-altered tomato and ranch-flavored dessert topping.
- There are 12,000 tiny bubbles rendered inside B.O.B. at all times.
What to Do Next
If you haven't watched this in a decade, it’s worth a re-watch just to hear the banter between Arnett and Rogen. Honestly, it holds up better than a lot of the CGI movies from that era because the comedic timing is so sharp.
Go check out the credits next time you watch. You'll see names like Amy Poehler (who voices the computer) and Jeffrey Tambor. It’s a masterclass in how to cast a comedy.
Start by looking for the "Code Nimoy" Easter egg at the beginning—it’s a nod to Leonard Nimoy that most people miss on the first pass. Then, pay attention to the Japanese katakana on the buildings during the alien broadcast; it literally just spells out "karaoke." It’s that kind of detail that makes the performances feel even more alive.