Discovering that he had the ability to persuade people into doing whatever he wanted while manipulating their senses as a child, Wayne Markley used his power to make millions, creating technology to enhance his powers even further, making himself- in his own words- a "more-than-perfect killing machine".
However, his life was changed when his son Jeremy died while trying to imitate his hero Spider-Man. Unable to accept that his powers couldn't help him, Fusion decided to take revenge on the wall-crawler, creating a false hostage situation by using his powers to create the impression that a mannequin was a genuine victim. When Spider-Man arrived, Fusion used his powers to give the impression that he had the power of Hulk, Thor and Mister Fantastic, killing two police officers by apparently taking control of their equipment and then killing over three hundred people with his bomb.
Although Fusion's attempt to accuse Spider-Man of the deaths failed, he left a message claiming that more bombs would go off unless Spider-Man met him for another battle at the warehouse where his son died. During this battle, Fusion apparently broke Spider-Man's neck, but Spider-Man realized that it was all an illusion when he managed to move his fingers, allowing him to easily defeat Fusion.
Some time after this, Fusion returned, now with Doctor Octopus as his apparent pawn, having discovered Octavius working in a factory under an assumed name. Having used Octavius to create detailed cybernetic limbs that could also control their owners by turning the systems that received information from the subjects' nervous systems into transmitters that could control them, Fusion arranged for various military officials to lose their limbs in accidents with the aid of a corrupt senator. This allowed him to subtly gain the necessary contacts to track down the controlling computer of the radiation-tracking satellite "John Hancock"- originally used to identify where nuclear bombs had been detonated, more recently used by General Ryker to track the Hulk- with the intention of using it to track Spider-Man's unique radiation signature and then kill him.However, after Fusion acquired the device, Octavius revealed that he had simply pretended to be weak in order to acquire the "John Hancock" device to sell it to the highest bidder, subsequently beating Fusion half to death as he derided the other villain's foolish belief that he could ever be so pathetic. After finding Fusion's mangled body, Spider-Man called an ambulance and subsequently tracked Octavius to a construction site, defeating his old foe and destroying the control device so that the satellite could never be used again.
Fusion has the ability to create the illusion that he has multiple powers and abilities (like the picture of him using the Human Torch and the Things powers at the same time). However, he is merely able to manipulate others' perceptions so that he appears to have these powers.
Once someone realizes that Fusion's powers are fake, they are apparently immune to his suggestions.