Kessler, leader of the First Sons, is the man who arranged for the activation of the Ray Sphere in the hands of Cole MacGrath, triggering the development of his electropathic powers.
Towards the end of the game, it is revealed that he is an older version of Cole who travelled back in time. In his own timeline he married his girlfriend Trish with his best friend Zeke serving as the best man, and went on to have several children.
In this reality his nemesis, "a Beast intent on destroying all life", attacked Empire City. In those early days Cole believed he could have defeated him, but instead fled, more concerned about the safety of his family. But after years of running, Cole's family is killed by the Beast, at which point it is too powerful for any force on Earth to defeat. Cole then utilizes his newest and most dangerous power, taking a one way trip back in time.
He then took up the name of "Kessler" and seized control of the First Sons, accelerating the Ray Sphere's development, spending years plotting and preparing the events that take place during the game. Even going as far as killing Trish so that the new Cole would never have a family to weigh him down with emotional attachments. Kessler's plan was to turn Cole into a saviour for humanity, developing his powers earlier, making him evolve faster and ultimately severing the emotional ties so he could make hard decisions and destroy the Beast.
After showing all of this to Cole, he collapses dead.
A skin is available in inFamous 2 that replaces the player model with that of Kessler, but he does not actually appear.