The Virtinoldor or Thrall-Noldoli were numbers of the Noldor who had become prisoners of Angband and were enslaved and forced to work in the deep mines and other facilities of Morgoths great northern fortress, and who were later freed by the deeds of their folk. Though not all of Morgoths Elvish slaves were Noldor, almost none of the Nandor and few of the Sindar proved to survive the brutal environment of the northern Underworld, without natural light and air. Some deceptive and often noble Elves had their will broken and they became Kaukareldar, or false Elves, willing Servants of the Dark Lord set free to spy out and confuse their masters enemies. Female Elves were said to have ended up as Drogwin, or slave-women, though the Elves found little evidence for this after Angbands fall and thus this may be propaganda of Morgoth. Most surviving Virtinoldor had suffered too much to be able to withstand the perils of Middle-Earth and left for the Undying Lands at the end of the First Age. The Thrall-Elves had even developed their own elvish dialect, Mulanoldorin.
See:
Known Virtinoldor[]
Finrod Felagund Edrahil of Nargothrond Gaurin Gimli the Blind Gwindor son of Guilin Loruin Maeglin Lómion Nargil Ogbar Rodrim Rôg of Gondolin Rúmil of Tirion Saithnar Salgant Tû