Insatiably curious about the first Well of Eternity, Lord Xavius bent all of his knowledge and effort to researching the Well's capabilities. He even went so far as to have his eyes removed and replaced with magical spheres that allowed him to see beyond the range of normal vision. Through his ambition and hard work, Xavius became Queen Azshara's chief counselor before the Great Sundering.
Xavius was the first Highborne to be contacted by Sargeras, creator of the Burning Legion. In moments Xavius had been enthralled by the dark titan. Sargeras swiftly corrupted the rest of the Highborne in the royal palace, including the queen, and convinced them to begin summoning Sargeras' demonic minions into Azeroth.
The War of the Ancients broke out, and Xavius remained one of the chief agents of Sargeras' will. At last Malfurion Stormrage called upon the power of nature to slay Xavius. Repeatedly struck by lightning, Xavius screamed in pain as he was destroyed in a violent thunderstorm. Even the cloud of dust that remained of his body was dispersed by an angry wind.
The counselor's failure infuriated Sargeras, who spent some time torturing the night elf's disembodied spirit as punishment. Eventually Sargeras decided that Xavius could still prove useful, and so Sargeras remade Xavius into a demon: the first satyr in existence. Only Xavius' eyes remained unchanged from those of his previous night elf existence.
Summoned back to Azeroth at Sargeras' command, Xavius gleefully used his new powers of persuasion and corruption to convert further night elves into satyrs, including Peroth'arn. He also encouraged dark thoughts of jealousy and ambition in Illidan Stormrage, thereby ensuring a chain of events that would culminate in Illidan's being imprisoned in a barrow prison for ten thousand years.
Primarily because he knew the deed would cause Malfurion great anguish, Xavius and a group of other satyrs kidnapped High Priestess Tyrande Whisperwind from the battlefield. In retaliation, Malfurion struck out with his druidic powers and caused an oak tree to grow inside Xavius. Even as the satyr swore that one day he would have revenge, the tree fed off his flesh and grew rapidly. In moments the tree had utterly consumed his body.
Millennia after the Satyr Lord met his end, night elves who know the tale of Xavius fear that some day he will manage to make good on his threat. To other satyrs, however, Xavius has become an object of worship: they hope he will return to Azeroth and lead them. Aside from demons, only a few warped individuals here and there pray to Xavius today, and they do so in the hope of being transformed into satyrs.