Mad Science in Easy Mode
A Mad Scientist as an antagonist is easy. He’s a cardboard cutout for your heroes to knock down.
He is typically:
Completely obsessed with his “Invention” which may be a weapon, or a technology that could be used to devastate the world, but he doesn’t care.
Craving recognition of his genius. Having invariably been drummed out of scientific circles due to his crazy theories, he is determined to eventually make a huge demonstration of his rightness once his invention is perfected. He’ll take over the world if he has to, although destroying a city or defeating a hero may do.
“Evil” possibly Chaotic Evil, in that scientific ethics or morals will not inhibit his actions in the pursuit of “Science”.
Reclusive, hence the exotic remote locations for his Lab, but also, nobody will miss him after you blow up his installation.
Short-sighted. Upon capturing the Hero, or the gang of Meddling Kids, he’ll prepare to incorporate them into his experiment, but fall way short on security. That especially includes information security, once he tells them his plan.
His invention or gadget is the stuff of Science Fantasy as opposed to Hard SF. It will typically defy at least one law of physics, if not all of them. And as we advance our knowledge into the quantum realm, it becomes ever more implausible to come up with a device that could be “real”. This is probably why the 1960’s and 1970’s were the heyday of mad scientist plots. We had the beginnings of technology like nuclear power, lasers, rocketry, computers, and robotics, all fresh and new and coming into the public eye without a whole lot of understanding. This is not to say that there was not already a long tradition of men of science meddling in God’s Domain. That goes back at least to Victor Frankenstein—the prototypical Mad Biologist/Necromancer.
In the 1950’s, nuclear radiation often created monsters, spontaneously and by accident, but it was in the 1960’s that Mad Scientists started to do it on purpose. The typical plot is just a modern update to Frankenstein’s Monster. He may have already built his first creature, but without the Radioactive McGuffin, he can’t yet bring it to life and then create an army of them to take over the world. Which is where the heroes come in to steal back the nuclear football. I’d love to see one where the McGuffin isn’t so easily portable, thus complicating the task of stealing it back.
The same often goes for robots. The Mad Roboticist will be obsessed with making the perfect robot soldier, but while the mechanics might be solid, a clever hero can usually take it down with a logic bomb, or “rewire” it into being good (was there nothing Valerie couldn’t do with a hairpin?). Vincent Price as Dr. Goldfoot pushed this in yet another direction, building sexy girl robots to seduce world leaders and then blow themselves up.
Physics defying rays are always popular. Aside from Death and Stun rays, you have Growth and Shrink rays, Heat rays and Freeze rays, Disintegration rays, Dimensional projectors (think Superman’s Phantom Zone prison), various Mind Control or Hypnosis beams, and of course good old Lasers, which could do any number of miraculous but likely destructive things.
For television and movies, Mind Control was popular because it was a cheap effect. Of particular note were various “mind swapping” devices, which you could find anywhere from Gilligan’s Island to Star Trek. The idea typically was to use the device to eventually swap out the mind of a world leader with that of a trusted minion, or the scientist himself.
Of course, we know today that this would never work. World Leaders would need minds to swap out first.
Speaking of Star Trek, the Transporter itself could have been used as a Mad Science device, but it wasn’t done intentionally. Such things were always played straight as a cost-saving measure in Science Fiction shows to get from place to place (see also Blake’s 7). But add a Teleportation booth and you get “The Fly”. I think the analog version in the original movie was actually more plausible for making its mistake than the computerized version in the Jeff Goldblum remake.
If your story is Science Fantasy enough to include super powers, your Mad Scientist’s obsession could become your hero’s powers. This is a good way to turn him into a recurring villain and your hero’s foil—the kryptonite your hero needs to not be a Mary Sue. See Doctor Sivana.
I suppose a more modern take on a Mad Scientist would involve the latest areas of scientific innovation, like Quantum theory, Nanotech, Genetic Engineering, Artificial Intelligence, and Wormholes. However, they’re harder to make exciting than a gigantic robotic golem with death beams coming out of its eyes. The latest science is great for technobabble, but it’s harder for the public to understand on the surface.
Mad Science in Hard Mode
Now take this cardboard cutout and make him your main character. Add complexity to his motivations. Humanize him, but give him a reason to shun societal mores without making him repugnant to the readers, unless you think you can pull off an anti-hero.
Order an extra case of Handwavium unless you’re an expert in practical quantum mechanics. You’re probably going to want to focus more on the character than the invention. The trials and tribulations of being a Mad Scientist is going to be more humanizing than having him play Ralf 124C41+ narrating the current state of technology to As-You-Know-Bob, who should already know this stuff.
He’s going to need rivals, but there he’s got plenty. Aside from fellow scientists, there are also the Heroes, Meddling Kids (with or without their Dog), and frankly, the whole world is against him. Sabotage, disloyal minions, evil organizations who hold the lease on his lab... and worst of all, the IRS. What, you thought you could steal the Mona Lisa and ransom it back to finance your experiments without the IRS taking its cut?
A love interest could be fun. Maybe he’s got a girl strapped to a table (Hey, it’s not real Mad Science until somebody gets strapped to a table) and falls in love with her as she bravely stares down the barrel of his Disgrontification beam. Maybe she’s an agent from the Forces of Justice™ who keeps sneaking into his lair because that’s the only way she can see him. Maybe it’s just the sweet girl next door who has no idea what he’s doing in the tunnels 500 feet below his basement, who would be devastated if she found out.
Come up with a reason he needs to succeed. Maybe he really does need to take over the world in order to free it from the lizardmen ruling it. Use your imagination. In fact, that’s required if you want to dabble in Mad Science.
Another hazard of writing Mad Science is keeping ahead. I published an RPG scenario centered on a Mad Science "Fear Projector." DARPA issued an RFP for one a few years later.
The fun thing about reading many fairy tales is that you keep running across the Mad Wizard's Beautiful. All right, he need not be a wizard. Ogre, devil, whatever. And she need not be his daughter. She could be a servant, or a captive.
The big difference is that the Mad Scientist does not have all the knowledge he craves and is looking for it. (Though I have heard scientists complain that he's really a Mad Engineer. He does not have a theory about destroying the Moon, he actually wants to do it.)