A franchise that has spawned five major entries across nearly twenty years is bound to have some degree of continuity. Thus, it's not uncommon for Elder Scrolls players to spot certain characters who have appeared in multiple titles. Whether or not these NPCs are significant to the main plot is irrelevant.
Some of these recurring characters are harder to find than others, however. A few have even managed to appear in almost every game in the series, which says something about their enduring popularity with both fans and developers alike. This list is by no means exhaustive, but contains some of the more choice selections.
10 Barbas
Barbas is the canine companion of Clavicus Vile, the Daedric Prince of pacts and bargains. Although dogs are often said to be "man's best friend," this doesn't seem to be true for daedra. Barbas and his master are frequently at odds with each other, with the protagonists often getting mixed up in their disputes.
Barbas has appeared as a dog in The Elder Scrolls II: Redguard, The Elder Scrolls V: Skyrim, and The Elder Scrolls Online. In The Elder Scrolls III: Morrowind he appears as the Creeper, taking the form of a scamp. His statue is present alongside Clavicus Vile's in The Elder Scrolls IV: Oblivion.
9 Dervenin
The Shivering Isles has no shortage of crazed inhabitants. Dervenin, the High Priest of Mania, is no exception. In The Elder Scrolls IV: The Shivering Isles he assists the player in relighting the Great Torch. He's thrilled if the protagonist decides to light the torch in favor of Mania.
Two hundred years later Dervenin can be spotted wandering about the streets of Solitude in The Elder Scrolls V: Skyrim. Empty black holes take the place of where his eyes should be as he rambles incoherently. It's up to the Dragonborn to decide whether or not to help the doddering, immortal madman.
8 Jiub
Jiub is a Dark Elf prisoner and the first character the player meets in The Elder Scrolls III: Morrowind. Along with the Nerevarine, Jiub is in the process of being released from jail when he promises to turn his life around. According to in-game lore Jiub later perishes at the onset of the Oblivion Crisis.
But the Dark Elf's story doesn't end there. While exploring the Soul Cairn in The Elder Scrolls V: Dragonborn the player can stumble upon the former prisoner, now known as Saint Jiub. It's learned that he redeemed himself for his past crimes by eradicating the Cliff Racers, a species of aggressive, flying hunters.
7 Karstaag
A fearsome Frost Giant from the island of Solstheim, Karstaag is a frightening creature to behold. Encountered in The Elder Scrolls III: Bloodmoon the Nerevarine must defeat Karstaag at the behest of the Daedric Prince Hircine.
Karstaag's appearance in The Elder Scrolls V: Dragonborn is treated as a bit of an easter egg. The Dragonborn can bring Karstaag's skull to his throne as part of an unmarked quest. Defeating the spirit of Karstaag grants the ability to summon him in combat as an ally. As if the Dragonborn needed another reason to be overpowered.
6 M'aiq The Liar
This fourth wall-breaking Khajiit is probably one of the more famous characters in The Elder Scrolls community. His interactions are very meta, often providing information on gameplay mechanics or even his own involvement in previous titles.
M'aiq has appeared in The Elder Scrolls III: Morrowind, The Elder Scrolls IV: Oblivion, The Elder Scrolls V: Skyrim, and The Elder Scrolls Online. Like his name suggests, everything this feline says needs to be taken with a grain of salt. His steady appearances in the main entries almost guarantees his inclusion in The Elder Scrolls VI when it finally releases.
5 Mannimarco
Also known as "The King of Worms," this Altmeri fiend's handiwork can often be found whenever necromancy is afoot. Mannimarco plays a large role in The Elder Scrolls Online as one of the secondary antagonists. The Vestige must battle the evil sorcerer in order to put a stop to the latter's plan of world domination.
Despite his defeat Mannimarco's soul survives to vex the Hero of Kvatch in The Elder Scrolls IV: Oblivion. He plays a role as the main villain in the Mage's Guild questline involving black soul gems and necromancy. Those with longer memories may also remember Mannimarco as a giver of quests in The Elder Scrolls II: Daggerfall.
4 Lucien Lachance
Lucien Lachance is a dreaded Speaker for the Dark Brotherhood in The Elder Scrolls IV: Oblivion. He is only too eager to induct those players with a more murderous bent into the shadowy group of assassins. Lachance plays a significant role in the Dark Brotherhood plotline, where he is eventually executed as a suspected traitor.
Fast forward to the time of The Elder Scrolls V: Skyrim and Lucien Lachance can still be found serving the Dark Brotherhood. Although his physical body is long gone his spirit is still more than willing to assist the player in their ghastly deeds. Summoning him as a spectral shade will assist the Dragonborn in combat whenever his help is required.
3 Neloth
This insufferable Dark Elven mage is a well-known (and dreaded) resident of Morrowind. He lords his superiority over anyone unfortunate enough who comes into contact with him. In The Elder Scrolls III: Morrowind he proves to the Nerevarine to be just as unscrupulous in his political dealings as he is in his personal affairs.
In The Elder Scrolls V: Dragonborn Neloth has moved to Solstheim in order to escape the destruction caused by the Red Mountain eruption. He helps the player in the quest to defeat Miraak, although his personality has not improved in the succeeding two hundred years.
2 Sinderion
Sinderion is a Nirnroot researcher and is the subject of possibly one of most frustrating and time-consuming quests in an Elder Scrolls game. When encountered in The Elder Scrolls IV: Oblivion he gives the Hero of Kvatch the quest "Seeking Your Roots." When all is said and done, 100 Nirnroots need to be collected to finish the quest, driving completionists insane in the process.
As such, few players may have wept when Sinderion is encountered again in The Elder Scrolls V: Skyrim. His corpse can be found in an old research station in Blackreach, evidently killed by the savage Falmer. The discovery leads to a new quest called "A Return To Your Roots" where thirty Crimson Nirnroots need collecting. Thus, Sinderion's legacy of tedium seemingly outlives him.
1 Uriel Septim VII
The Emperor of Tamriel himself, Uriel Septim VII's influence can be felt in nearly every game in the series. He sets into motion many of the main questlines in the franchise, including The Elder Scrolls: Arena, The Elder Scrolls II: Daggerfall, The Elder Scrolls III: Morrowind, and most famously in The Elder Scrolls IV: Oblivion.
His untimely death in the fourth entry precluded his appearance in The Elder Scrolls V: Skyrim. An argument can be made that Uriel Septim VII is perhaps the most important character in the franchise due to his actions in the earlier games, whether they are witnessed onscreen or not. Maybe he will even be included in The Elder Scrolls VI somehow. Who knows?