Aan Taanu's past history is unrevealed. Aan Taanu is described in the mystic tome, the Anten Decan, which the Beyond Reason Spiritual Fellowship used to summon him to earth. Aan Taanu possessed the dragon Fing Fang Foom, whom he used as his vessel on earth. Hildreth, high priestess of the cult, sought to merge with him. Aan Taanu summoned her to his dream realm (probably either an astral, or his own dimension), where he mated with her in order to father a new race which would take over the world. Omen organized the Legion of the Night and transported them to this realm to prevent this. Hildreth was already pregnant in far along in her term (magic, you know), but Arianne Wright tore the unborn fetus from her womb, killing the fetus and Hildreth at the same time. Omen then threw his magic sword into AT's head, banishing him back to his realm and preventing his immediate return. Fing Fang Foom then plunged into the New York Harbor and disappeared (apparently making his way back to the Valley of the Sleeping Dragon, where he is almost always found, as if he's been asleep ever since he first appeared back in Strange Tales).
Some time after this, Aan Taanu attempted to gain revenge on Omen for his role in his defeat. Aan Taanu sent a demon to possess Morton Klasser, a recently released convict from Ryker's Island. The demon strengthened Klasser's urges to kill Leena Wolfe, a private investigator hired by Klasser's former wife to document his affairs and abuses. Wolfe had recently been hired by Allison Lamb, a fashion editor, and former girlfriend to Charles Blackwater, the host to Aan Taanu's former servant, Omen. Lamb had hired Wolfe to investigate the changes in Blackwater. However, Omen learned of this and temporarily entered the form of Leena Wolfe. When Klasser arrived to kill Wolfe, the demon instead forced him to attack Lamb in order to cause pain to Omen's host, Blackwater. Omen emerged from Wolfe and forcibly removed the demon possessing Klasser and blinded it, causing it to kill itself while trying to fly back to Aan Taanu.