Anyone who has quested in the Storm Peaks should be familiar with the story of Thorim, his wife, Loken, the Sons of Hodir, and Veranus. You, the player, actually have a hand in getting Thorim from where he is at the Temple of Storms, into Ulduar under the control of Loken and Yogg-Saron. Need a refresher? Allow me to paraphrase. Beware that if you have not done the quest chain, the following is a spoiler.
The quest chain starts from a Goblin in K3 about the large blue women (aka the Hyldnir) who took the Goblin men prisoner. You go off to save them and in the process get involved with the Vry'kul ladies and their war with the Sons of Hodir. Disguised as a big blue woman yourself, you proceed to take part in their games to see who will be the champion and rule by Thorim's side.
After jumping around on the backs of dragons flying around the Temple of Storms, you prove yourself and end up in front of Thorim himself. Oddly enough he seems a bit coo coo. At first he thinks your his wife, Sif, but then recognizes you for the
Thorim was originally one of the chief watchers over Ulduar, the Terrace of the Makers, and the races of frost. Loken, Thorim's brother, killed Sif, Thorim's wife, and blamed it on Amgrim, the king of the Frost Giants. Thorim, in his rage, through his hammer at Arngrim, killing him, but before Arngim died, he was able to put a rune on the hammer, preventing anyone, including Thorim, from using it. Thorim then retreated to the Temple of Storms in a stupor of despair.
Taking your arrival as a sign, Thorim wakes from his stupor and begins to plot against the real villain, Loken. First you mend the relationship with the Sons of Hodir and Thorim by working for them some. In return you manage to get Thorim his armor and hammer back from the spirit of Arngrim. Once things are all patched up with them, you then set out to get Thorim his epic mount back. This is Veranus, the brood mother of the local proto-drakes who Thorim had released into the wild before he went into his stupor.
Armor, check, hammer, check, proto-drake mount, check. Okay! Off you and Thorim go to Loken's throne at the Temple of Wisdom. Thorim and Loken exchange some trash talk and a little fisticuffs, but Loken cheats and a strange tentacle gasps Thorim and Veranus. Thorim and his drake are taken off to Ulduar. Loken laughs at you and reveals that he was the blue woman inside the mine who got you started on this whole quest chain to begin with. In thanks, he doesn't kill you.
Loken has Ignis fuse some metal plates onto Veranus, creating Razorscale. Razorscale flies around Razorscale's Aerie in Ulduar, causing problems for some of the Explorer's League members who are there. A sad end to a noble beast.
Thorim resides in the Halls of Lightning where he is still plagued by visions of Sif, his long dead wife, presumably thanks to Yogg-Saron.
A lot of the mythology of Thor lines up with Thorim. They both had wives named Sif, were betrayed by their brothers and had named hammers. Apparently Thor was defeated by a Jormungar as well, and we see one of these when we enter the arena where Thorim is standing in the Halls of Lightning.