The Mad Thinker is a Marvel comics supervillain. He is a genius specializing in evil robotics and usually comes up with very elaborate infallible devious plans that unfold like clockwork (until they don't).
It seemed that his primary objective had not really been to take over the city but to manipulate organized crime into helping him get into the Baxter building so that he could indulge his intellectual avarice by stealing the technology of Reed Richards. In that sense, the Fantastic Four did not really defeat him, they only defeated his pretext. The Mad Thinker would gladly get sent to prison for a peek at the secrets of what he considered the greatest mind in the world.
Prisons don't do well to hold the Mad Thinker and he escapes from all levels of incarceration with little difficulty. Often he doesn't even bother escaping, but simply transmits his thoughts into a robot body at one of his secret bases. He can not only do his work, but he has the perfect alibi—he's already in prison.
After his initial defeat against the Fantastic Four, the Mad Thinker teamed with the Puppet Master for the first time. He used the original X-Men through a mind-controlled Professor X to battle the Fantastic Four. Again with the Puppet Master, he pitted the Thing against the Human Torch, but was foiled by Reed Richards.
He then created Quasimodo, a "living" computer. He located and revived the original Human Torch and used him to battle the present-day Torch. Later, with his Triumvirate of Terror (Piledriver, Hammerhead, and Thunderboot). He captured the Avengers, and invaded Avengers Mansion, but was foiled by the unexpected intervention of Hercules, who had only recently begun to stay with the Avengers following his exile from Olypmus.
The Mad Thinker impersonated Dr. Jose Santini, and disrupted an attempt to cure the Thing, causing the Thing to turn against the Fantastic Four. However, the Mad Thinker was captured by Mister Fantastic and the Human Torch. From his prison cell, he sent a battle android against the Fantastic Four, but the android was sent into the Negative Zone by Mister Fantastic.
He allied with the Puppet Master again and with Egghead in their attempted blackmail of the United States government using a laser-firing satellite. Again with the Puppet Master, he attacked the Fantastic Four using androids of their past foes. With the Puppet Master, he then battled Spider-Man and the Thing.
The Mad Thinker then took part in the Black Lama's contest of super-villains by was defeated by Iron Man. Mad Thinker the re-established control of his robot the Scavenger and sent it against the Fantastic Four. He was defeated by Thundra, Tigra, and Brute. He then battled the Thing, Daredevil, Vision, and Yellowjacket. With the Puppet Master and Wizard, he attempted to disrupt the wedding of the Human Torch and Alicia Masters. The Mad Thinker later took control of the computers in Fantastic Four headquarters, but was foiled by Mister Fantastic.
The Mad Thinker later refused involvement in Loki's "Acts of Vengeance." He instead escaped prison, and sent Gargantua against Wonder Man and the Wasp in an attempt to forestall the proposed Super-Powers Registration Act. Later, he attempted a robbery using robot dinosaurs, and was foiled by Destroyer and Tattletale of Power Pack.
The Mad Thinker became interested in the young super-group called the New Warriors, and posed them a riddle when they first formed. In the final issue of the series, the answer to the riddle was revealed: the Mad Thinker's nephew had accidentally gained uncontrollable superpowers from his lab, killing his mother in the process. Now, the Thinker wanted them to help him. Presumably they did so using the Neo-neutralizer they acquired in that adventure.
Since then, the Mad Thinker has been seen battling She-Hulk in a prison escape attempt. However, this Mad Thinker was revealed to be merely yet another android duplicate of the real Mad Thinker. Following the destruction of this android, the Awesome Android (now calling itself Awesome Andy) took custody of the android's still-functional head until it was stolen by the teenage supervillain Southpaw.
Although willing to kill heroes who get in his way, there are lines the Mad Thinker will not cross. A partnership with the Wizard was cut short after the kidnapping of the child Franklin Richards. The Wizard wished to experiment upon Franklin and learn the secret of his vast powers. The Mad Thinker, however, claimed that this had an almost certain probability of Franklin's death. When the Wizard acknowledged this but decided to continue anyway, an angry Thinker dissolved the partnership and helped lead Franklin's godfather, The Thing, to where the Wizard had the boy hostage. Currently, the Mad Thinker has himself allied with the Puppet Master, planning to strike against the Fantastic Four yet again. Told that he preferred to be called "The Thinker", The Puppet Master asked him why he had been called "The Mad Thinker" in the past. The reply was that he used to have "repressed anger issues". When the Puppet Master asks him about his anger, he replies that "it isn't repressed any more." He has built a device to amplify the Puppet Master's power so that they can escalate a battle between the two rival factions in the Super Hero Civil War.
In exchange for not being connected to the crimes on Yancy Street, Reed has the Thinker double check his calculations concerning the potential effects of not supporting the registration of all superheroes.
His analytical, mathematical, and geometrical abilities are of a sophisticated order not commonly found on Earth. He is particularly adept at computers, robotics, and artificial intelligence, with Ph. D.s in computer science and engineering. He has constructed his own android, The Awesome Android, and once resurrected the original Human Torch. He also built Quasimodo and the Scavenger, and various other equipment as needed, including monocle-sized hypno-lenses. In addition to his own achievements he has stolen much of the secret technology of Reed Richards, back in the incident when he took over the Baxter building.
The Mad Thinker is also a proficient disguise artist. Through a surgically-implanted radio link, he is able to project his consciousness into an android simulacrum of himself.
The Thinker's intricate plans are most often foiled by what he refers to as the x-factor, or human unpredictability. Also the Thinker is not an intuitive genius (e.g., Reed Richards) and is thus incapable of true invention; instead, he synthesizes for his own use the creations of others (e.g., his android creations are based on discoveries of Reed Richards).
She also appeared as the villain in the Ultimate X4 miniseries, which showed her with an android resembling the Awesome Android, which she calls Robby. During this appearance she attempted to steal Cerebro and use it to gain control of all the minds on the planet, but, with the aid of Wolverine, Shadowcat and Iceman, the Fantastic Four were able to distract her until Reed could reprogram Cerebro to cause Rhona to develop the power of empathy rather than control, forcing her to shut Cerebro down or lose herself amid the pain of the world.