Board Thread:Suggestions forum/@comment-29212138-20170526182111/@comment-25754873-20170527012629

When he found how greatly his knowledge was admired by all other rational creatures and how easy it was to influence them, his pride became boundless. By the end of the Second Age he assumed the position of Morgoth's representative. By the end of the Third Age (though actually much weaker than before) he claimed to be Morgoth returned

-Letter 183

I thought it was in the Apipendix, it was in his letters.