Milliardo Diel'Zaram is a lesser noble from Silvermoon. He lived his early years as a dilettante, and moved to Dalaran at age 80 to learn "a smattering more of magic."
While studying magic in Dalaran, he learned of a minor religion known as the Belief of Quel'Anu (Kuu-el-AH-nu) (The High Sun) amongst the elves, but the humans and others reffered to it as the Church of Solyumon (Sahl-yuu-Mahn). He began looking into it, and found "the sun." He converted to the Belief just months before the fall of Dalaran.
When news that the Burning Legion was assaulting Silvermoon, he made his way back as safely as possible. He found the city in ruins. He fled back to Dalaran to see if aid could come, but found Dalaran in a heap, along with the vast majority of the Church leadership of Quel'Anu gone, either having fled or died. He rallied what he could, but thought the two cities he called home "insufferable for the church at the present." He and the remaining hierarchy held a quick vote, and he was chosen as it's head (something he actually did not expect, but took with glee). He led them to Stormwind, which held the second largest number of followers, and established a temporary seat of power there. However, when news of Silvermoons revival arose, he went north and established "The First Seat," or official "capital" of the church. He allowed Stormwind to carry the mantle of "Second Seat."
He then heard news of the island just off the coast that was catering to those of Silvermoon who wished to further there powers. He went in hopes that by showing that the head of the church was seeking to further himself, then perhaps the faithful would also rise from their near stupor.
He quested like so many others, and did increase his power. He can currently be found in Silvermoon, preaching to the faithful, and attempting to spread the faith.
Milliardo is the head of a small religion known as the belief of Quel'Anu (the High Sun). It is unique in that it caters to both the Horde and Alliance by attempting to remain neutral. However, events in Stormwind may cause a split in the church. Archbishop Tobaricus of Stormwind is currently advocating that the Alliance members null their "corrupt contract to those who preach from afar," and has also taken the title of "Reformer and Head of the Church within the Alliance." He bases this on the hostilities between the Horde and Alliance, and believes that the Seat should be in Stormwind. The Archbishopric Council is currently deciding on whether or not to acknowledge Tobaricus's title as Archbishop, or to strip him of his rank (which might just urge the Church based in Stormwind to secede anyway).
Plans are being drawn up by Milliardo to possibly move the Seat to Dalaran in Northrend
More info on the Church later.
Milliardo is unique in that he is not really a Blood Elf, but has been tainted by the Fel magics around him (meaning that had he not been in Silvermoon for as long as he has, he would not have the characteristics of a blood elf). He does not pledge himself to Kael'thas or Silvermoon, though the city is the current seat of power for the Church and would no doubt defend the city.