The Last of the Ancients is a tome found in Act V of Diablo III. Written by Kalmor, it is dropped in Passage to Corvus (fake version) from the Ancient's Satchel after Kalmor is defeated. Obtaining the journal will add to the Field Research achievement.
It reads as follows:
When I look upon our weakened offspring, I am filled with rage. Killing them is a mercy, but one I have been unable to extend to myself. I must seek another to do what I cannot, before the endless days drive me to madness.