Aside from being a very powerful archmage, Flattery also had perfect knowledge of Finder Wyvernspur's repertoire of songs and the ability to sing them (if not quite at his creator's level of perfection). He could morph into a dragon at will, raise the dead, and commanded a flying castle.
Flattery was created by Finder, but not raised properly. He was beaten (and possibly worse) when he failed to live up to expectations. Having a mature body and a childlike mind at the time, he had no way to deal with this and eventually lashed out. He became obsessed with destroying Finder and all associated with him. His second victim was Finder's other apprentice, whom he drove to suicide.
In his growing madness, Flattery found it more and more impossible to behave normally. His mania caused him to launch powerful magic at a portrait of Finder, to swing Cat around like a ragdoll and so on.
In the end, he wanted not to be so much like Finder, to not constantly be reminded of what he was, how badly he was treated, etc.
Despite having been endowed with Finder's memories, songs and skills, Flattery as a newborn could not live up to Finder's quality standards. Finder grew angry at his imperfect creation and struck out. Flattery never sang again, causing Finder to alternate between beating and pummeling the construct. One of his apprentices felt pity and let Flattery out. Flattery attempted to exact revenge upon Finder, but the ray of disintegration caught the apprentice instead. Flattery escaped whilst Finder, overcome with guilt, spoke not of his success at creation and took the blame for his apprentice's death on himself.
For the next few hundred years, Flattery hid in the shadows, becoming a powerful mage and yet enjoying destroying evidence of Finder's existence. Some years before the Time of Troubles, he had amassed an army near his castle and sought to conquer. Cole Wyvernspur fought him and at the cost of his own life and stopped Flattery for the nonce.
In 1358 Flattery found Cat and in return for her "missing" memories got her to enter the family vault to recover the Wyvernspur for him. He then vaporized Jade Moore, another sister of Alias. He tried to enact his mad scheme for revenge by wiping out the Wyvernspur family. Giogioni Wyvernspur, Olive Ruskettle, Drone Wyvernspur and Cat eventually managed to defeat him.