Was Glorfindel of Rivendell the same as Glorfindel of Gondolin?
[This updates question V.D.2 of the Tolkien LessFAQ.] Yes. With the publication of The Peoples of Middle-earth, certainty has become possible: the first essays in the section “Last Writings” of that book discuss Glorfindel and his history. Those texts make it very clear that after his death in the flight from Gondolin, Glorfindel was re-embodied in Aman (see question III.B.6) and was later sent back to Middle-earth as an aid or an emissary. Tolkien seems to have been uncertain as to whether he returned in the Second Age by way of Numenor or in the Third Age as a companion of Gandalf.