No livro, Gandalf sabe sobre Gollum porque Bilbo disse à empresa - embora ele primeiro tenha retido informações sobre o Anel:
Then they wanted to know all about his adventures after they had lost him, and he sat down and told them everything-except about the finding of the ring ("not just now" he thought). They were particularly interested in the riddle-competition, and shuddered most appreciatively at his description of Gollum. (Out of the Frying-pan, Into the Fire)
Eventualmente, após o episódio das aranhas ( Flies e Spiders ), Bilbo diz tudo aos Anões (deve-se notar que Gandalf não faz parte da empresa neste momento):
There they lay for some time, puffing and panting. put very soon they began to ask questions. They had to have the whole vanishing business carefully explained, and the finding of the ring interested them so much that for a while they forgot their own troubles. Balin in particular insisted on having the Gollum story, riddles and all, told all over again, with the ring in its proper place.
Eu não posso atualmente fornecer uma referência em O Hobbit para quando Bilbo contou a Gandalf sobre seu Anel (embora Gandalf soubesse sobre Gollum como minha primeira citação mostra), mas Gandalf evidentemente sabia, e soube bem cedo, como é mostrado in A Sombra do Passado em O Senhor dos Anéis:
Then I heard Bilbo's strange story of how he had "won" it, and I could not believe it. When I at last got the truth out of him, I saw at once that he had been trying to put his claim to the ring beyond doubt.
Quanto a Sauron, não há absolutamente nenhuma evidência de que Sauron sabia alguma coisa sobre a posse de Gollum e Gollum do Anel antes da entrada de Gollum em Mordor, mas depois disso ele descobriu rapidamente o suficiente; novamente de Shadow of the Past :
'But I am afraid there is no possible doubt: he had made his slow, sneaking way, step by step, mile by mile, south, down at last to the Land of Mordor' .....
'Wretched fool! In that land he would learn much, too much for his comfort. And sooner or later as he lurked and pried on the borders he would be caught, and taken – for examination. That was the way of it, I fear. When he was found he had already been there long, and was on his way back. On some errand of mischief. But that does not matter much now. His worst mischief was done.
'Yes, alas! through him the Enemy has learned that the One has been found again. He knows where Isildur fell. He knows where Gollum found his ring. He knows that it is a Great Ring, for it gave long life. He knows that it is not one of the Three, for they have never been lost, and they endure no evil. He knows that it is not one of the Seven, or the Nine, for they are accounted for. He knows that it is the One. And he has at last heard, I think, of hobbits and the Shire.'
Então, sim, Gollum simplesmente entrou em Mordor.