Upon the world of Nirn, in The Elder Scrolls universe, all manner of Man, Mer, and Beast live their mortal lives. This is illustrated well within the games because of the plethora of race options players have in the character creators. Despite this, there are actually even more sentient races that could just as easily be playable.
But whether it is being separated by oceans or the disappearance of a people, there are sound reasons for why they are non-playable. Who are these species/sub-species, and how they fit in the story of The Elder Scrolls?
10 The Kothringi Of Black Marsh
A sub-species of humans who were natives of Black Marsh, they are notable for their greyish skin that is described as "metallic" and "reflective" in appearance. Their origins lie in the history of the Ayleids and how they, along with many other diverse groups of humans, were kept as slaves. After the reign of the Ayleids, they settled in Black Marsh, becoming distinct from their brethren. They worshipped their own pantheon of gods and lived more tribalistic lives.
Unfortunately, they were all but wiped out by the Knahaten flu outbreak of 2E 560. The only Kothringi that still "live" are the inhabitants of Stillrise village, but they are merely immortal undead who made a pact gone wrong with the Daedric Prince, Clavicus Vile.
9 The Tang Mo Of Akavir
The Tang Mo are a race of "monkey people" that inhabit The Thousand Monkey Isles of Akavir. Like many things in Akavir, despite the wealth of history between it and the continent of Tamriel, very little is known about this race of beastmen. Interestingly enough, the term "Tang Mo" is Akaviri in origin. It translates to "Thousand Monkey Isles", so they are so named by the very place they inhabit.
Beyond this, it is known that they have fought off several enslavement attempts, particularly by the Kamal, and that in recent history, they have allied with the Ka Po'Tun. Most accounts describe the people generally as "brave, simple, and insane".
8 The Orma Of Black Marsh
If the Kothringi seemed sparse on historical details, then the Orma are quite literally an entirely different breed. Another sub-group of mankind, the Orma are notable for being a race without sight. Members were born either blind or without eyes at all, typically wearing blindfolds. Outside of that, all else that is known is that they lived primarily in Black Marsh, and that they all died out due to a cause that is still unknown.
There is only one historical account of an Orma figure, the tribeswoman Catchica. She was alive during the First Era and played some kind of role in the Reman Empire when they fought against the Dumner led by Vivec. Nothing more is known.
7 The Ka Po'Tun of Akavir
The Ka Po'Tun are the Tiger-Dragon people of Akavir. That is not to say that they are part-dragon but they have enslaved dragons, they are obsessed with becoming dragons, and their current leader, Tosh Raka has actually managed to become a dragon. It is said he is colored like a tiger and is the largest dragon in the world.
In the most recent excerpts of the lore, it is known that they control a powerful empire in Akavir, and their current goals are to destroy all of the "vampire snakes" (the Tsaesci). Once this is done, they plan to invade Tamriel.
6 The Maormer Of Pyandonea
Tamriel is no stranger to elves. The Altmer, Bosmer, and Dumner are only a portion of the many types of people who fled Aldmeris for Tamriel. Enter the Maormer (also known as Sea Elves), a historically jaded, elven people who inhabit the southern continent of Pyandonea. The key distinguishing features that separate them from their kin are their milky white eyes and their colorless, translucent skin that seems to almost have chameleon-like properties.
It is said that the Maormer wished to settle in Tamriel as well, however, they were exiled shortly before the great exodus from Aldmeris. The Maormer ended up on the significantly less hospitable continent of Pyandonea, while the Altmer claimed Summerset. The Maormer apparently still hold resentment towards the Altmer for this fact.
5 The Lilmothiit Of Black Marsh
Another race that has mysteriously vanished from the history of Tamriel, the Lilmothiit were a group of mammalian beastmen, possibly related to the Khajiit, who were described as being vulpine in appearance. Like many of the peoples that used to call Black Marsh home, it is possible they were wiped out by the Knahaten flu, which killed almost every non-reptilian creature in the province during the Second Era.
Another theory purports that the Argonians drove them off of the continent. Whatever the case, it is more likely that they are not dead, as they were described as being a nomadic people. This implies that they probably left the continent, though for what reason, one can only guess.
4 The Imga Of Valenwood
A native species of beastmen in the land that is now known as Valenwood, the Imga or "Great Apes" are a dexterous people that can scale trees as easily as other peoples walk upon the ground. It is believed their society thrived before the arrival of Mer on the continent. After this historical event, the Imga slowly regressed culturally, choosing instead to idolize the elves, particularly the Altmer.
Imga wore extravagant clothing, took care to enunciate their speech, and even dueled with swords to emulate their overlords. In 2E 582, the Imga vanished from Valenwood. One author claimed they fled to escape the Three Banner War and Planemeld during the events of The Elder Scrolls Online. They have since returned, but where they went and how long they were gone remains a mystery.
3 The Sload Of The Coral Kingdom
Described as the most hated race by the people of Tamriel, the Sload are a group of slug-like beastmen that live in the Coral Kingdom of Thras off the west coast of Tamriel. They are famous for their mastery of necromancy and are believed to have existed on Nirn since its earliest days.
The Sload are hulking and slow, making them not the greatest warriors. Their threat truly lies in their magical ability which they have used to conjure sea-beasts, undead armies, and even a plague that devastated the population of Tamriel during the First Era. This additionally lends something towards their level of intelligence. In the few interactions the Tamirelic people have had with the Sload, they describe the slug creatures as self-centered, amoral, and even sociopathic.
2 The Kamal Of Akavir
Meaning "Snow Hell" in the Akaviri tongue, Kamal is the name of both the nation and the people that inhabit it. They are described as a race of demons who "thaw out once every year" to launch attacks against the other peoples of Akavir, the Tang Mo most of all. They have always been driven back, only for the cycle to repeat.
They even attacked most of northern Tamriel once, starting their invasion in Windhelm and moving east into Morrowind. They were led by their king, Ada'Soom Dir-Kamal, and by the time they were defeated, it took the formation of the Ebonheart Pact, along with the aid of Almalexia and the Underking, to finally stop Dir-Kamal's invasion.
1 The Tsaesci Of Akavir
The Tsaesci are perhaps the most famous non-Tamrielic race to exist on Nirn, at least from the perspective of the people of Tamriel. This is not surprising considering the Fighters Guild was founded by a Tsaesci, as well as the famous Blades. A Tsaesci and his son even ruled the Empire for a time as Potentates during the transitionary period between the First and Second Eras. The total amount of time comes out to around four hundred years.
Described as "vampiric serpent folk" by the peoples of Akavir, they are brilliant military strategists as well as accomplished warriors and mages. So impressive was their skills that after their hard-won defeat at the hands of the Empire, the Emperor granted amnesty to all survivors and integrated them into the Empire, which many contribute towards the success that followed.