Born of the brief union of the War God Ares with the goddess Aphrodite, Deimos (his brother) and Phobos dwelt principally in the Netherworld, from which they intended to aid their father in the destruction of the Earth, and thus the hated Amazons, as well as the other Olympian Gods.
At first Phobos attempted to slay the Amazon Princess Diana, who had been chosen by combat and the Gods to oppose Ares' plans, by bringing to life the creature called Decay, but the Amazon Princess destroyed Decay after a savage battle across the city of Boston.
At length, the Princess Diana, accompanied by four humans who had befriended her, brought the battle against Ares to the Netherworld itself. Here she confronted Deimos and Phobos, and a struggle to the death began. During the course of the battle Deimos attempted to poison the Amazon with the venomous bite of his serpentine hair; venom that would fill the Princess Diana with blind, unreasoning terror.
In the last seconds before she could succumb to the venom, Diana hurled her razor-sharp tiara at the gloating Deimos, and Decapitated him. The cowardly Phobos, fearing for his own life, fled into the darkness, swearing vengeance on the Amazon Princess.
Phobos returned to exact revenge upon Diana months later with the help of the Gorgon, Euryale. Together they captured Hermes, the messenger god, and unleashed on Boston, Ixion the mass murderer - who he had freed from Hades. Diana fought the villians and freed Hermes. Together they destroyed Euryale and Ixion and Phobos was imprisoned for his crimes in Tartarus.
During the War of the Gods, Circe released Phobos and enlisted his help in destroying the Gods and Creation itself. Phobos awakened the Aztec god, Quetzalcoatl and sent him to attack a villiage in South America. This brought him to the attention of Superman and Starman where the heroes beat him. Phobos, being a coward at heart, retreated to Areopagus, the fortress home of his father Ares. Here he murdered his sister Harmonia before running back to Circe side on Olympus. When the battle turned, he abandoned his allies and vanished.
Again seeking revenge against those who had stood in his way. Phobos reappeared in Gotham City. This time inhabiting the body of Scarecrow. Here he resurected the spirits of his slain brother Deimos and sister Eris and placed them in the bodies of Joker and Poison Ivy. The three siblings sought to make Gotham into a new Aeropagus, a base for their father Ares on earth. Phobos hoped this plan would gain him favour in his fathers eyes. Wonder Woman, Batman and their allies fought the gods but during the battle Phobos took over the Batman, making the ultimate god of fear. Wonder Woman freed Batman from Phobos influence and in front of his father, Ares. The God of War was disgusted by his sons incompetance yet again and ripped his children's spirits from their human hosts and banished them back to Tartarus.
Nox posed as the goddess of love and beauty, Aphrodite, and seduced Ares, the god of war. Nox, according to her plans, later gave birth to two sons, Deimos, the god of terror, and Phobos, the god of fear. Deimos and Phobos were raised by Nox to do her bidding. Centuries later in modern times, they were both sent to apprehend Thor and Hercules. In the battle, both of the brothers were killed.
Not being able to live with the death of her sons, Nox utilized the power of human fear during the Great Fear takeover by the Fear Lords in order to resurrect her sons. They held Clea and Rintrah in their captivity, but were both again killed due to the lack of fear in the humans caused by Doctor Strange, this time at the hands of their prisoners.