The Mad Thinker has spent his life discerning the future by calculating all of the known variables he can possibly think of. Using these calculations, he can predict where lightning will strike, where a person will step, or where a bullet will hit. Not wanting to battle superpowered foes personally, he employs robots and traps to deal with those he has calculated would interfere with his plans.
After turning to a life of crime from boredom, the Thinker set his sights on the Fantastic Four. He brought all the powerful crime bosses to New York City in order to become the 'King of Crime' as their leader. With his massive collection of computing machines and his incredible mind he planned to take over the city and make it a separate nation with him in control. In an elaborate scheme, he was temporarily able to divide the Fantastic Four and gain access to their headquarters, the Baxter Building. With Reed's technology he created the Awesome Android and turned it against the Four. He was defeated when he failed to plan for what Reed Richards called the 'X-Factor,' or the unknown, when Reed had a safeguard and deactivated all of his weapons. Once captured, the media dubbed him 'the Mad Thinker', which he despised.
Since then he has a grudge against the Fantastic Four and planned revenge. He has teamed with other villains and sometimes offers himself as a consultant to other criminals. He joined the super villain group known as the Intelligencia. Together they stole the lost information of the Library of Alexandria. Once they had all the info, they were betrayed by Doctor Doom and the team disbanded.
The Mad Thinker was also responsible for building the Cosmic Hulk, although the idea to build it came from a program created by Galactus known as the Cosmos Automation Program that was designed to help Galactus easily consume the Earth..
The Mad Thinker was recently contacted by the Future Foundation to find a way to defeat Reed Richards, alongside The Wizard, The High Evolutionary, and others.
In the Ultimate Universe, the Mad Thinker is a young woman named Rhona Burchill. She is jealous of Reed Richards since he got into the Baxter Building Program for gifted children instead of her. She used some of her brother's brain matter to increase her brain power, and has a disfigured head as a result of it. She speaks aloud almost constantly in a stream-of-consciousness style as a side-effect from the augmentation.
Later on she stole Cerebro's CPU chip and augmented her mind. Unfortunately for her the result was superhuman empathy with others, which she detested. She was seen at that time with a robot named Robbie and her face was normal again, though she was still unstable. She was apparently killed when her escape vehicle was sabotaged by Wolverine and it exploded.