Mercer Frey, the leader of the Thieves' Guild, is voiced by Stephen Russell, the voice of Garrett, the infamous protagonist and master thief from the Thief series of games.
General Tullius is a gruff, no-nonsense officer who is practical-minded and does deep down care about his men and Skyrim itself. He shares these traits with one of Michael Hogan's other roles - Saul Tigh in Battlestar Galactica. Unlike Colonel Tigh, however, Tullius doesn't seem to have alcohol problems. He also looks extremely similar to Captain Bailey, another one of Hogan's roles. He's found inside Castle Dour, and Hogan is known for playing dour characters.
Tullius' second-in-command, Legate Rikke, was also a serious female military officer... on a certain space station.
Paarthurnax teaches the player one of the words of fire breath. He's also voiced by Charles Martinet, who's far better known as Mario.
A very subtle one: In Farkas's bedroom in Jorrvaskr is a lute, which he presumably knows how to play. In Markarth, the Dragonborn can encounter Yngvar the Singer, an accomplished bard. Both characters (among others) are voiced by Michael "Popeye" Vogelsang, the guitarist and lead singer of the somewhat obscure band Your Favorite Train Wreck.
Serana, the female vampire who accompanies you throughout most of the Dawnguard questline, is voiced by Laura Bailey. This isn't the first time she's voiced a vampire or a magic user.
The similarities between Serana and Rayne border on plain Shout-Out at times.
Miraak is voiced by Peter Jessop, who's best known as the voice of the ReaperSovereign. Guess what happens when you touch the pillars without proper magic?
Beam Me Up, Scotty!: The famous quote from the guards actually goes "Then I took an arrow in the knee", not "to the knee" as it's often quoted.
Christmas Rushed: It is very possible that this game suffers from it. When fans looked at the game-files with the Level Editor, it was revealed the creators planned to implement complex quests and scripts that sadly did not make the final cut. Examples are a dynamic civil war, an arena in Windhelm, and a questline to help Mjoll the Lioness bring down the Thieves' Guild. Many of these were probably cut because the game had to be released on November the 11th 2011, so the creators did not have enough time to implement all of their plans. As a result, many of the storylines in the game feel rushed when compared to earlier installments of the franchise. Fortunately, though, modders came to the rescue, and many of the cut quests have been restored, most notably the civil war and arena.
Doing It for the Art: If you no-clip past the borders of Skyrim, you'll find you can walk all the way to Morrowind and Cyrodiil. They're not at all detailed, just height maps with generic textures and a few landmarks (like the White Gold Tower), but they're still there... even though you'll never be able to reach them without cheats or, theoretically, Game Mods.
Much of it is there for those instances when you can see beyond Skyrim from within the game's proper map. There are plenty of places inside Skyrim that do this, too. If you no clip through the walls of a city, you'll see a partially detailed map of the city again to provide the detail you'd see from certain vantage points even though the city interior is a different map. Likewise, when you're within a city, the exterior of Tamriel is all detailed this way, again to provide what you'd be able to see from within city walls. There's a mod called "Open Cities" that moves some of those cities into the Tamriel map. The Dragonborn DLC takes place in Solstheim, the island just north of Vvardenfell, where the events of Morrowind took place.
Fan Nickname: "Odie" for Odahviing. Similarly, we have "Paarthy" (or just "Paarth") for Paarthurnax.
Gallus Desidenius has earned the nickname of Amazo from some due to how similar the former's mask and the latter's face look.
No Export for You: The Collector's Edition was essentially this for Australia, selling out within hours of being put up for pre-order due to the incredibly small number of copies allocated to the country. As something of a compromise, Australia had its own exclusive Limited Edition, as a free upgrade for EB Games pre-orders.
Similarly Named Works: Hircine's Daedric quest shares its name with the 1957 film Ill Met By Moonlight, based on the novel of the same name. They're unrelated, but all have the same origin; the phrase is a quote from Shakespeare's A Midsummer Night's Dream.
If the file names seen in the editor for their equipment are any indication, the Stormcloaks were originally going to be called the Sons of Skyrim, with their officers being called the Sons of Talos.
It seems that the Civil War was originally going to have several new features, such as all five main holds being attacked by their opposing side, as well as new radiant quests. At least some of these features were restored with this mod.
According to rumors, there was going to be a Dark Brotherhood sidequest where Erikur commissions you to assassinate Elisif so he can become Jarl of Solitude. Thankfully, it never made it past the cutting board. An alternate take on that sidequest, "Boethiah's Bidding," was supposed to be a sequel to "Boethiah's Calling" and involved the same task. Some of the code is actually in the game, but the fact that it was never fully implemented makes the quest Unwinnable even if you force-start it with the console.
According to Todd Howard, shortly before working on Skyrim, Bethesda were in talks to make titles based on A Song of Ice and Fire; but, despite some heavy interest, they ultimately turned it down in order to continue developing The Elder Scrolls and their own lore. The return of the dragons and the Civil War in Skyrim (plots that feature heavily in both works) may also have been partially inspired by this, although this has yet to be confirmed by any official sources.
Miraak, from the Dragonborn DLC, had a bunch of lines cut from the final game. These lines make him more of an Anti-Villain (such as regretting having to kill you), and even hint that he was originally slated to live at the end of the main quest.
Mephala's Daedric Quest has some cut content that implies that Jarl Balgruuf would have been killed by his own children, with his brother Hrongar taking over as Jarl. Remnants of this are still hinted at within the quest, and the plot of Balgruuf's son having been corrupted by Mephala is never resolved.
Considering the dropped Balgruuf and Elisif murders in game, Skyrim as originally written would have been much more pro-Stormcloak, ultimately leaving the Empire with only one Reasonable Authority Figure Jarlnote Idgrod of Hjaalmarch, who's probably going to die of old age soon, with the remainder being scheming backstabbers. While Elisif's murder was dropped early in development, Balgruuf's made it all the way to early beta testing. It was ultimately the beta testers who pointed out that killing off reasonable authority figures on the Imperial side, especially the one who trusts the Dragonborn from the start of the game, made choosing to go Imperial a Shoot The Shaggy Dog Story and would ruin the moral ambiguity of the Civil War storyline that's loved today.
Ingun Black-Briar's use of the phrase "It's a fine day with you around" after you complete her quest suggests that she was intended to be a potential Love Interest, but this was scrapped. This is also true of Elisif.
Mjoll the Lioness was going to have a lengthy questline in which the Dragonborn helped her take down the Thieves' Guild, along the lines of "Destroy the Dark Brotherhood," but this was scrapped for time. This is probably the reason that Mjoll has an essential flag - like many quest-giving NPCs, she was to remain unkillable until after the completion of her quest, and you can't complete her quest because you can't ever begin it.
Word of Saint Paul: The idea that the Thalmor want to end Talos worship as part of a plot to destroy the mortal world and Ascend to a Higher Plane of Existence doesn't actually appear in-game (beyond some strong hints from Esbern), but comes from forum posts by Michael Kirkbride. While responsible for a lot of Elder Scrolls lore (especially Morrowind) and the creation of the Thalmor originally (they are referenced in the first Pocket Guide to the Empire that was packaged with Redguard), he was not directly involved in writing the plot of Skyrim beyond the initial idea stages (that happened during Morrowind and early Oblivion).
Wes Johnson voices both the ghost of Lucien Lachance and Emperor Titus Mede II. This is really the only case where Talking to Himself potentially occurs, since you can summon his ghost to assassinate the Emperor in the Dark Brotherhood questline.
Lynda Carter voices the Nord hero Gormlaith Golden-Hilt in Sovngarde and the Daedric Prince Azura.
Craig Sechler plays the Daedric Princes Hircine and Peryite.
Lani Minella is Nocturnal and the Night Mother. Talk about an evil resume - and this is on top of her providing the low, husky voice for female dark elves.
It's kinda surreal to talk to Elisif's servant, Erdi, and then find out that Elisif herself sounds exactly like her.
This is why some fans headcanon that Erdi is either related to Elisif, or perhaps serves as some sort of impersonator for the Jarl in case of an emergency.
There is one point in the Thieves' Guild questline where Mercer can follow the player all the way to the general goods store in Whiterun. It is almost startling to hear two characters with such differing personas sharing the same voice actor.
Gideon Emery is encountered twice in the Dark Brotherhood questline - he voices both Arcturus and Commander Maro's son Gaius. He also voices a few random Imperial archers who can be met on the road.