Lloigor

The Lloigor (loy-gor) were a group of Pre-Universe beings with some connection to the Great Old Ones or possibly being another name for them. As the Old Ones were the equivalent of Time Lords, the Lloigor may have been analogous with the Outsiders or Shobogans.

They were not native to this universe, but one of them, the Animus, got into it. The effort and energy spent on doing this meant the others would be unlikely to try the same thing. (PROSE: The Dark Path) This involved passing into a parallel universe that would survive for a fraction of a second before the destruction of the previous universe and after the beginning of the current one. (PROSE: All-Consuming Fire, PROSE: Millennial Rites)
 * Depending on whether or not the Lloigor and Old Ones are the same beings, the Doctor's comment that others would not enter seems odd since he encounters several Old Ones. However, this is the Second Doctor who says it, indicating that he will be proven wrong upon learning of the Old Ones from Matrix.

They possibly all had a similar appearance or biology to that of the Animus, which was frequently identified as Lloigor, (PROSE: All-Consuming Fire, PROSE: Millennial Rites, PROSE: The Dark Path, PROSE: Divided Loyalties) "Animus" being the name given to it on Vortis. (PROSE: Twilight of the Gods)

Behind the scenes

 * August Derleth created the singular Lloigor. Colin Wilson created the plural Lloigor, a race of invisible energy beings that could manifest as dragons and "sea-devils". In Wilson's story, they are associated with the names of obscure Great Old Ones that H. P. Lovecraft named in stories he ghost-wrote. The protagonist of Wilson's story concludes that Derleth's Lloigor got its name from the race.
 * Both Grant Morrison's Zenith and Alan Moore's The League of Extraordinary Gentlemen use the term Lloigor to identify Great Old Ones created by Lovecraft or Derleth.