Alexander Montez
Dr. Bruce Gordon
Jean Loring
Note: Eclipso has apparently possessed countless other less notable hosts or notable hosts for a short period of time.
Pre-Crisis
Menace
Post-Crisis
God of Vengeance
Lords of Darkness
Pre-Crisis
Unknown
Post-Crisis
Luna: Fortress on the dark side of Earth's Moon.
Transformation into a malevolent being by an Eclipso Diamond granting superhuman strength, speed, stamina, agility and durability capable of projecting beams of frigid black light through the diamond.
Note: In the pre-crisis version of Eclipso the transformation was triggered by any eclipse either natural or artificial and was reversed by exposure to burst of bright light.
Note: Montez controlled the power and nature of Eclipso by tattooing his body with a series of glyphs and incantations.
Pre-Crisis
Eclipso Diamond: Apparently alien gem which can channel the spirit and powers of Eclipso.
Post-Crisis
Eclipso Diamonds: Gems carved from the Heart of Darkness which was once the physical body of Eclipso. When a possessor of such a diamond feels wrath then they channel the malevolent spirit and are transformed into Eclipso.
Dr. Bruce Gordon
Eclipso Vol. 1 & 2
Green Lantern Vol. 2
House of Secrets Vol. 1
JSA
Phantom Stranger Vol. 2
Pre-Crisis
Filming a solar eclipse on the South Pacific island of Diablo, Dr. Bruce Gordon was confronted by a local witchdoctor who attempted to kill Gordon for defying local customs. Lunging at Gordon with a dagger he missed his target but he cut the doctor with a strange black diamond clutched in his other hand. The momentum of the witchdoctor's lunge carried him over the ridge Gordon had setup his camera equipment and the would-be killer fell to his death.
The grateful natives bequeathed the witchdoctor's costume and black diamond to Gordon - which turned out to be a curse in the end. When Gordon witnessed his next solar eclipse he was transformed into the villainous Eclipso.
Post-Crisis
The spirit of God's wrath was first released upon the Earth to express the supreme deities displeasure with humanity and punish sin during the time of Noah. When God's chosen, Noah, released a dove to see if there was dry land after the rains the malevolent spirit killed the bird of peace and was cursed. The malevolent entity's body was transformed into a large black diamond known as the Heart of Darkness and its evil spirit was trapped upon the dark side of the Moon.
Millennia later the Heart of Darkness was found in Africa and carved into thousands of smaller gems. Now whenever a possessor of an Eclipso Gem has feelings of wrath and anger their dark nature emerges and they are transformed into Eclipso.