The Great Demon King, he was sealed away for 1000 years after his mortal body dies on the battlefield. Drwc resurrected him using Riannon as living sacrifice, but is instead killed after Arawn saves Riannon from mind control. She takes a liking to him instantly, and makes him chieftain of the Gael Tribe. Arawn's true (magic) name Lucifer, he was the 13th Angel born after the previous 12, and thought to be an imperfection. He became 1 of the 12 Angels after his "father" Angel, Myrddin died by performing the Song of Creation. He followed in the footsteps of his "father" Angel and opposed the remaining 11 White Angels, thus leading him to be exiled from Heaven and became a Fallen Angel. He was the one who freed Primula, and Humans from the bindings of the White Angels, as they had cursed mankind to praise and worship their creator till death. Throughout the ages, the White Angels hated him and opposed him on every occasion possible, eventually leading to his "death" after being struck by a cannon blast from a siege weapon, which the element used is Electrum (Arawn's physical body is weak against this element). He then went into a deep sleep to recover his mortal body for the next 1000 years prior to the start of Tears to Tiara.

(Source: Wikipedia)