Akaviri

There several theories about Men of Akavir, that they died out long ago, were eaten by the Tsaesci (The connotation of "eaten" may not mean physical digestion, see the quest Lifting the Vale for more info), or that they are the Tsaesci (as suggested by some books in The Elder Scrolls V: Skyrim).

Where They Came From
It is not known exactly where the Men of Akavir came from, but some say they were Nedic (or Nede) settlers like the ones that settled in Tamriel. This is entirely possible, because if the people of Atmora migrated to Tamriel, then they most likely also migrated to Akavir. Wherever they did come from, they are gone now, as they were eaten long ago by the Vampiric snake-people of Tsaesci. As mentioned before, eaten may not refer to literal ingestion - we simply do not know.

What They Looked Like
As their name implies the Men of Akavir were just that,men.While it has not been confirmed what their skin color was they definitely looked like all the other races of Men in terms of shape.

Culture
Little to nothing is known about the culture of the Men of Akavir, other than the fact that they seem to heavily mirror Asian culture through their armor, weapons, and buildings. (Cloud Ruler Temple is based on Akaviri design, as well as the armor of the blades. The Akaviri also seemed to have used katanas, a traditional Japanese armament).

History
Again little to nothing has been preserved of the culture of the Men of Akavir.On the box art of Morrowind and in-game is the Akaviri war banner. However, it is only known for a fact that the Tsaesci used this banner and the Men of Akavir may or may not have used it. Since they died out a very long time ago almost nothing past this is known about the Men of Akavir.