From Tolkien Gateway
Gorgumoth was the hound of Mandos, according to the early version of the legendarium in The Book of Lost Tales. It is said that he guarded Melko, bound in Lumbi, after his defeat in the Battle of the Silent Pools.
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Book of Lost Tales Part Two, "VI. The History of Eriol or Ælfwine and the End of the Tales", outline 1, p. 278