Firestorm I
Alter-egos: Ronald Raymond, Martin Stein
Controlling Personality: Ron
Group Affiliation: Justice League of America
Home City: Pittsburgh (formerly New York)
Height: 6'2"
Weight: 202 lbs.
Eyes: White (no pupils)
Hair: Inapplicable (fiery corona)
Powers: Firestorm can see the atomic structure of objects. He can alter the atomic structure of any non-organic object - changing density, elemental make-up, or making it a new object entirely. He can alter his own atomic density, fly at great speeds, and become intangible. He can project bolts of nuclear energy as nuclear blasts and absorb most forms of radiation. He can exist in a vacuum. While intangible he cannot activate his other powers.
Regular Comics Run: Firestorm I 1-5, Firestorm II 1-64, annuals 1-5
Other Important Appearances: Crisis on Infinite Earths, Flash, Justice League of America, Legends

Firestorm II
Alter-egos: Ronald Raymond, Martin Stein, Mikhail Arkadin
Controlling Personality: Martin
Group Affiliation: Justice League of America
Home City: Pittsburgh & Moscow
Height: 6'2"
Weight: 202 lbs.
Eyes: White (no pupils)
Hair: Inapplicable (fiery corona)
Powers: Same as Firestorm I
Regular Comics Run: Firestorm (vol. 2) 65-85, annual 5
Other Important Appearances: Invasion!, Millennium

Firestorm III
Alter-egos: Ronald Raymond, Mikhail Arkadin, Svarozhich
Controlling Personality: his own (none of his alter-egos control him)
Group Affiliation: none
Home City: none
Height: 6'2"
Weight: 202 lbs.
Eyes: White and Red Flames
Hair: Inapplicable (fiery corona)
Powers: Same as Firestorm I, but the elemental Firestorm also has absolute power over fire - control, production, and absorption - and his matter transmutation powers can affect organic matter with no ill effect to himself. However, his matter transmutation powers can be unstable as the elemental Firestorm. The elemental Firestorm is also very, very hard to kill, because he is an elemental being.
Regular Comics Run: Firestorm (vol. 2) 85-100
Other Important Appearances: The Janus Directive

Firestorm IV
Alter-ego: Martin Stein
Group Affiliation: none
Home City: none
Height: 6'2"
Weight: 202 lbs.
Eyes: White and Red Flames
Hair: Inapplicable (fiery corona)
Powers: Same as Firestorm III
Regular Comics Run: Firestorm (vol. 2) 100
Other Important Appearances: Extreme Justice, Green Lantern: Circle of Fire, War of the Gods

Firestorm V
Alter-ego: Ronald Raymond
Group Affiliation: Justice League of America, The Power Company (former)
Home City: Pittsburgh and Ivy Town
Height: 6'1"
Weight: 179 lbs.
Eyes: White (no pupils)
Hair: Inapplicable (fiery corona)
Powers: Same as Firestorm I, however because he no longer has access to the knowledge of a physics professor (Stein or Arkadin), his matter transmutation powers are limited to what Ron has learned.
Regular Comics Run: Extreme Justice 0-17, The Power Company 11-17
Other Important Appearances: Day of Judgment, Green Lantern: Circle of Fire, JLA, Identity Crisis

Ronald Raymond
Occupation: student, model
Home City: Pittsburgh and Ivy Town
Height: 6'1"
Weight: 179 lbs.
Eyes: Blue
Hair: Brown
Marital Status: Single
Known Relatives: Edward Raymond (formerly Rockwell, father), Elaine Rockwell (mother, deceased), Felicity Smoak Raymond (stepmother), Richard Dare (AKA Captain X, natural grandfather, deceased), Patricia Rockwell (grandmother, deceased), Ted Rockwell (grandfather, deceased)
Regular Comics Run: Firestorm I 1-5, Firestorm II 1-100, Extreme Justice 0-17, The Power Company 11-17
Current Status in the DC Universe: believed killed during the events of Identity Crisis, spirit believed to have passed on after assisting Jason Rusch

Martin Stein
Occupation: former fire elemental, formerly a physics professor and nuclear physicist
Home City: none, formerly Pittsburgh and New York
Height: 5'10"
Weight: 161 lbs.
Eyes: Brown (though they often appear blue in the comics)
Hair: Gray
Marital Status: Divorced
Known Relatives: Clarissa Clemens (ex-wife)
Regular Comics Run: Firestorm I 1-5, Firestorm II 1-100
Current Status in the DC Universe: part of the Firestorm matrix with Jason Rusch

Mikhail Denisovich Arkadin
Occupation: nuclear technician, professor
Home City: Moscow
Height: 6'0"
Weight: 180 lbs.
Eyes: Gray
Hair: Brown
Marital Status: Married
Known Relatives: Nina (wife), Irena Arkadin (daughter), Sofia Arkadin (daughter), Alexander Arkadin (brother), Dmitri Arkadin (brother), Sylvia (sister-in-law), Serafina (niece)
Regular Comics Run: Firestorm II 61-100, Firestorm III
Current Status in the DC Universe: operating quietly as a superhero in Eastern Europe

Jason Thomas Rusch
Occupation: college student
Home City: Detroit
Height: ?
Weight: ?
Eyes: Brown
Hair: Black
Marital Status: Single
Known Relatives: Alvin Rusch (father), Sylvia (mother)
Regular Comics Run: Firestorm III 1-23
Current Status in the DC Universe: operating as Firestorm with Martin Stein

Pozhar
The name Pozhar, meaning "destructive fire," was given to Mikhail when he exhibited meta-gene superpowers after being exposed to radiation from the meltdown at Chernobyl. Pozhar was shown to be able to fire intense fireballs, create lava geysers, and fly by creating a tremendous amount of heat that provided lift. However, he had to be encased in a suit as a containment vessel, otherwise his own heat was killing him. After Mikhail merges with Ron and Martin to form Firestorm II, he does not become Pozhar or manifest these powers again until Firestorm (3rd run).

Svarozhich
A clone created by the Russian government using cells obtained from Firestorm II, Svarozhich was a creature with power but without a soul or conscience. He initially manifested the elemental powers of Firestorm and then absorbed the nuclear powers from Firestorm II. Ron and Mikhail merged with Svarozhich to create Firestorm III, thereby giving the elemental a human spirit and conscience. Svarozhich briefly reappears in Firestorm #100 after Firestorm III releases Ron and Mikhail from the matrix, but is destroyed as part of the plan that enables Martin Stein to become Firestorm IV and defeat Brimstone.