Mikhail Denisovitch Arkadin originally was an intellectual attached to the Chernobyl power plant, and was present during its catastrophe; his metagene was activated, and he gained the ability to create an all-consuming fire. Unfortunately, that same fire destroyed most of his body, and he was forced to wear a containment suit in order to prevent himself from destroying everything he touched. The Russian government then maneuvered him into position to be one of its premier heroes, placing him into a battle against the original Firestorm, who was then calling for complete nuclear disarmament.
The battle raged for a time between the two heroes, until a nuclear weapon was dropped on the duo while they fought in the Nevada desert. From that debacle arose a new Firestorm, in which Mikhail played a crucial role, along with the original two members of the Firestorm Matrix, Martin Stein and Ronnie Raymond. He continued as a member of Firestorm in another incarnation, as an Elemental, but was eventually removed from the Firestorm Matrix so that Martin alone could bear the powers. Ronnie and Mikhail returned to their homes, depowered.
During the "In My Father's House" storyline in the most recent Firestorm series, it was revealed that Mikhail is, in fact, once again in control of his former abilities. He was re-powered by a nuclear test gone wrong in Russia. After going by the name of Firestorm for a time (not knowing that a new Firestorm made up of Jason Rusch and Martin Stein had been in operation for some time), he has now changed his super identity back to Pozhar.
The New 52
Professor Mikhail Arkadin helped Professor Martin Stein invent the Firestorm Protocols.
Powers, skills, abilities, and paraphernalia
Pozhar acts as an energy tranformer, absorbing massive amounts of energy or radiation, and firing it back out in the form of fire, heat, or nuclear blasts. He also retains some of the powers of the original Firestorm, such as flight and density control, though they were not part of his power set initially. He no longer uses a power suit, as he can now create his costume out of pure energy.