First Introduced during a GM event in Everquest 1, then again in Lost Dungeons of Norrath, Mayong has constantly been trying to make himself a god through the manipulation of Norrathians.
He is the final kill in the Depths of Darkhollow expansion as well as the prime problem solver in The Buried Sea.
He is thought to have been an Elddar elf, or even an elf from a time before that Elddar age. Because of this the origins of his vampirism are shrouded in mystery. There have been whisperings throughout the age that he had started to dabble in necromantic magics. Shunned by his peers for trying to find a way to make his life eternal, and not in the Mother's good graces, he sought out the Father of Hate. Making a pact, much like Venril Sathir, he was given eternal life and thusly became the first Vampire. Because of this gift from the Father Mayong started to grow hateful and withdrew back into the Faydark. Obsessed with becoming more powerful in his now "immortal" state he gathered many around him. Teir'Dal were by then starting to become fierce creatures to be reckoned with. He surrounded his castle with them, hoping to fend off visitors or adventurers from entering there as he kept to himself and his studies.
Being immortal he saw the dragons as one of his only enemies as they were powerful and also immortal. The Ring of Scale was his primary target. Mayong considered the dragons of Kunark as a threat to his ambitions so he sent dracnids (seemingly half Teir'dal half spider) to spy on the Ring of Scale. The more sedcluded Claws of Veeshan weren't seen as a threat, but he still sent dracnids to Velious, in addition to Kunark, to keep track of them and also the giants there as well. He lost contact with them long ago and it's believed that they no longer follow his orders at all. Queen Dracnia of the Crystal Caverns is believed to have been an original member of Mayong's spy ring.
It was not long before he found one who was as obsessed with ambition as him. The Teir'Dal and Enchantress of Neriak Tserrina Syl`Tor caught his attention while trying to achieve immortality herself. The Tower of Frozen Shadow in Velious was going to become a new vampiric stronghold and getaway for herself and her soon to be life partner and husband, Mayong. This was also in line with his plots as he was able to keep a closer watch on the dragons of Velious from there. Tserrina was granted the "gift" of vampirism by Mayong Mistmoore during their engagement, which ended up having dire effects on her due to her previous spell attempt at immortality. She ended up sprouting bat wings, and her beauty began to fade as her face cracked like stone. Mayong departed from the tower, using her reaction to the vampire blood as his excuse to depart, with the promise he would return on their wedding day. When he did not return, Tserrina tried to leave the tower to find him, only to realize the Tower was, in fact, a prison for her. In her rage, she extended her curse to all the denizens of the Tower, and slowly drifted further into insanity, vowing to exact her revenge on Mayong on the day she was finally freed from the Tower.
Another unfortunate student of Mistmoore's was Khasra Vei'Ras who was taken by Lanys T'Vyl (who was by then the chosen Child of Hate). Enraged by the kidnapping of his follower he came to the aid of the King and Queen of Neriak to mess up the plan of Lanys to complete the Staff Malevolence; a weapon thought to either be Innoruuk's own weapon or a weapon that would destroy the Prince of Hate. In the middle of a ceremony to complete this artifact Mayong thwarted Lanys' plan and left her for dead after taking the object himself and handing it over to the archpriest of Hate, Dorvias N'Keth. Lanys was then saved by Innoruuk and became his Chosen, being raised to Demigod status. Mayong not concerned with the affairs of Neriak or Primordial Malice, left with his student as it was no longer his concern.
After this it is said Mayong secluded himself inside of his Castle. Some say he was not even there, that he had abandoned all that he created in search of something. That 'something' everyone was lead to believe was some ancient artifact or artifacts that were going to help Mayong on his thousands of years search to ascend to Godhood. Rumors were started of seeing him move into the Underfoot. Others think that he went into the Plane of Hate to find another artifact. Some have even conjectured he was in one of these two places when the Planes themselves closed holding Mistmoore back... until now. (and then the EQLive/EQ2 timeline split happens~)
Now he reigns once again as the leader of Castle Mistmoore where only the bravest adventurers dare to tread. Some conjecture he may be again trying to find a way to ascend to his godhood, some say he might have already found such. Who knows what would come to pass if he was indeed able to do such. Being so involved with the vile doings of Norrath it is certain the world would never be the same again.