Hodir is a watcher of Ulduar, just like Thorim, Freya, and Mimiron. He had resided in the Temple of Winter in the Storm Peaks, but by the time we get there, he is gone, his servants are dead and the place smells of sulfur. This would indicate that Fire Giants, the mortal enemies of the Ice Giants, had something to do with Hodir's disappearance. The only known Fire giants exist as bosses in various instances/raids. Ignis is a Fire Giant. Whether they were actually involved is not known. What is known is that Hodir is now in Ulduar, under the control of Yogg-Saron, via Loken who betrayed all of the watchers. Hodir is found in the Halls of Winter in Ulduar.
Prior to that, Hodir had been a guardian over the Ice Giants, who themselves had taken on the name "Sons of Hodir" to identify with their patron. The Sons of Hodir play heavily into the Thorim quest line as I mentioned before, so it's interesting to me that the Sons of Hodir seem to have more connections to Thorim in game than Hodir.
There has been some speculation that Hodir is the inspiration for Greatfather Winter of the dwarves and Winter's Veil.. He makes mention to the "Veil of Winter" when you request his help against Yogg-Saron.
Other than that, there's not much else to say about him, which is surprising since there's a whole faction named for him in the game.
Freya is the last watcher of Ulduar. She is known mostly for being in tune with nature, and watcher of all things living. Our first encounter is with her is actually the Avatar of Freya, an aspect of Freya that she separated from herself and left in charge of watching over the life in Sholozar Basin. We interact with the Avatar via several quests in the basin centered around repelling the scourge that are spilling into the basin from Icecrown.
Freya had resided in the Temple of Life in Storm Peaks. Currently all life there is dead, including the plants. There is evidence of a battle that took place there between Freya and a being of similar size. I assume this to be Loken, but it could have been any of the beings within Loken and Yogg-Saron's control.
Within Ulduar, Freya is found in the Conservatory of Life with her three guardians. The area is still lush and vibrant, despite it's watcher being corrupted. However, all of the animals and plant life are now hostile towards players.
The last thing I'll say about Freya is that she is referred to as a "Daughter of the Titans." There is some speculation on whether or not the watchers are actually Titans. Is the daughter of a Titan, a Titan? Maybe, but it could just be a title instead of an actual family link. I maintain that the watchers are not actual Titans, but creations of the Titans for specific purposes. There is a quest in Storm Peaks that implies the watchers are Titans though, so there is that to consider.