Abaddon was one of the Six Human Gods, a fallen predecessor of Kormir. His sphere was Water and Secrets, which were later absorbed by Lyssa and Kormir, respectively. He is also associated with Depths, Knowledge and Magic.
Abaddon is notable for warring against the other five gods when they were compelled to seal magic back in the Bloodstone they had released it from. Eventually, Abaddon and his followers, the Margonites, were cast out of Tyria, into the Realm of Torment, a realm within the Mists which would act as his prison, as his power could not be destroyed. Afterwards, the gods erased almost all knowledge of the fallen god, and departed the world of Tyria in an event known as the Exodus, which the Mouvelian Calendar is based on. The Forgotten race would then stand watch over Abaddon's prison.
Over a thousand years later, in 1075 AE, the maddened god was close to breaking free from his prison, a plan which was undone by the Order of the Sunspears and Order of Whispers in Elona – Abaddon was finally destroyed for good while Spearmarshal Kormir absorbed his power, becoming the Goddess of Truth, and preventing Abaddon's former power from running rampant.
Prior to his final defeat, Abaddon was responsible for many disasters which plagued Tyria, including the Searing of Ascalon, the Cataclysm of Orr and the Jade Wind of Cantha, as well as many tragedies which occured indirectly as a result of those events, such as occupation of Kryta by the White Mantle and their mursaat overlords, which led to the Krytan civil war. Abaddon created strife against and within the human race for many centuries, manipulating the Charr in their invasion of northern human kingdoms of Ascalon, Kryta and Orr, and ultimately causing civil war in Elona which, aided by his humanborn worshippers, which nearly resulted in his release. The other deposed human god, Dhuum, and the evil half-brother of Balthazar, Menzies, also aided Abaddon in his efforts on almost all fronts, and especially in the Mists. Since his attempted return, known from prophecy as the Nightfall, and ultimate death, nothing has been heard of Abaddon's followers or allies.
Like the other gods, Abaddon's origins are shrouded in mystery. According to the Margonite Apostate, Abaddon gained his power from an older, deposed god. Like other human gods, he also had a temple in Orr, the Cathedral of Hidden Depths, which now lies sunken in the Straits of Devastation.