Abaddon has always been a brash and powerful man. During his time alive, he had many enemies and some speculate that he once held a position of power and was perhaps of a royal family. Very little is known about him and he likes to keep it that way. He says little beyond what hes made others expect of him and he tends to keep his motivations simple.
When the Plague Bloodlines started forming he was the first to take the initiative and slaughtered an entire young clan. Further action was halted by his peers as he was feared to be abusing his power, and it was unsure of whether or not the plagues should be adopted by the cursed clan, or even given their own place at the table of the 6. Abaddon was displeased with both of these options. In his mind they were a threat and a virus. A mistake that needed to be wiped from existence.
Abaddon lead a crusade against the plagues and in doing so has become a legend to be feared in their ranks. Because of his deep dislike for plague's and the way his peers were handling the problem, he became very hostile towards Belial, their creator. His fiery ambition was often foiled by her calm and level-headed temperament. His divergent behavior lead to his inevitable downfall. Around the time of Dracula's ascent to power in the world of the undead, Abaddon was trapped and entombed in his coffin and hidden away in hopes that he would never again walk the earth.
Abaddon held awesome strength and intimidation. Where other vampire's might call on their abilities to mesmerize or allure prey, he instead developed his ability to produce a feeling of crippling fear. That coupled with his incredible strength magic made him a powerful vampire.
Abaddon was the first vampire to use/teach his clan the power of demonic runes, symbols of the demonic language eternally etched into the flesh of the user. These symbols allowed for near instant spell activation at the cost of increased need to feed and weaker mental fortitude.