The Lucid Dream. The Monster in your Nightmares. The Fiend with a Thousand Faces.
The Old God of Death.
That's him in all his tentacled glory. Yogg-Saron is indeed an Old God and one of the ancient beings responsible for the curse of flesh which afflicted the Titan creations and gives us the races we know today. The Titans themselves could not destroy the old gods without destroying the world of Azeroth, so instead, they imprisoned them. Ulduar is the prison of Yogg-Saron. That is it's purpose, and that's why we've come here to begin with. Because the prisoner has gotten loose.
That's really about all of the history we have for old Yoggy. Of course, we know there's lots of stuff currently going on. For one, Yogg-Saron is free, but has not physically moved himself out of Ulduar. I'm not really sure how he could without legs... although I guess he could move around on his tentacles. He's been doing a lot of work through the watchers that he's corrupted however. I started with Loken, who was the chief jailer. Loken then was used as a pawn to capture and corrupt the remaining keepers, and even uses us, the players, in his scheme to get Thorim. What he needs all of the keepers for is unclear, other than to get rid of the people that could prevent him from completely breaking free.
By the time we get to Ulduar, we've already encountered much of the old god throughout Northrend. In the Grizzly Hills we see Vordrassil, the world tree of Northrend is destroyed and laying in pieces. Thousands of years ago the ancient druids planted this tree to be the first world tree, but the roots went to deep and entered the domain of Yogg-Saron, corrupting the tree, and prompting the Druids to destroy it. This tells me that Yogg-Saron has some domain over the deep places of the earth and this is further reinforced by the whispers you can here when entering the mines of Icecrown.
The faceless ones seem to be at the command of Yogg-Saron, and also come from the deep places of the earth as seen in the dialogue with the Nerubians. And then to top it all off, we have SARONite. The Tuskarr call it the Black Blood of Yogg-Saron, and it is believe that it is an actual by-product produced by the old god. Saronite, the metal has very magic resistant properties, especially holy magic, and thus was chosen specifically by Arthas, the Lich King, to construct the many gates and towers throughout Icecrown, and the armor and weapons that are used by the Scourge. But prolonged exposure to Saronite has maddening effects. Miners forced to excavate Saronite in Icecrown can be seen leaping to their deaths and mumbling in an insane matter. Who knows what effect all the Saronite will have on the scourge?
The only other confirmed old god was C'thun, who was locked up inside An-Qiraj until relatively recently. He was killed, but there are rumors that while his body was destroyed, his presence remained, and now the Twilight Cultists have descended up on the ruins in an attempt to resurrect him. So now, even though Yogg-Saron has been defeated, and the keepers of Ulduar liberated, can we be sure that he is completely dead? Or will his presence somehow remain, manifested throughout Icecrown via the saronite deposits. And just what is the connection between the Old God of Death, and the Lich King?
During the fight with Yogg-Saron, some people must enter his mind and witness three different visions. These seem to be visions of events that Yogg-Saron was present at. Or at least it makes sense that he would have been if he has the memories of the events.
The first event is the creation of the Demon Soul by the five dragon flights during the War of the Ancients. Ultimately, this was done by Neltharion and was a catalyst for his corruption into Deathwing. So was Yogg-Saron the old god behind Deathwing's creation? Perhaps the death of Yogg-Saron is a precursor to the reemergence of Deathwing coming in the Cataclysm.
The next event is Garona Halforcen's assassination of King Llane. This was ultimately the reason that the humans lost the war against the invading orcish hordes during the first war. Without their leader to guide them, the humans fell apart. We know now that Garona was being controlled by the Twilight Cultists when the assassination occurred. And the cultists are worshipers of the old gods. So again, Yogg-Saron is telling us of his involvements of these events.
The final scene is not one that we are familiar with from history, and seems as if it may have occurred much more recently. The Lich King stands before an immolated champion and a prisoner, torturing the champion and trying to break him to his will. Who is the champion, and who the prisoner? Some say it may be Bolvar and Saurfang the younger. Others speculate the Lich King refers to Arthas, whom he broke when he joined with the Lich King. Yogg-Saron's involvement in this vision is more vague. Is he in league with the Lich-King? Or opposed to him. As Yogg states, "He will learn... no King lives forever, only death is eternal!"
There's still a lot of mystery surrounding Yogg-Saron, and I hope that we get a few more insights into what happened at Ulduar down the road. Perhaps a connection will be made when we go to Icecrown. Or during the cataclysm with Deathwing.