Volotham Geddarn, the infamous book writer and troublemaker, but still a human.
In his bio page, there are publishing dates for some of the other books (in the 1300DR) but not for the "latest" guide to monsters.
Is there anywhere a reference to when the book is out? It seems the 5e campaign is set in the late 1400DR so it may or may not be a century between them.