This is a direct translation by me of the text next to “The Art of Diablo”:
This book presents more than 500 remarkable artworks from Diablo, Diablo II, Diablo III and Diablo IV, which were created for the iconic aRPG series by Blizzard Entertainment that brought nightmares to many generations of fans.
The text on the book itself states that the foreword/introduction in the book is done by Chris Metzen.
This is 100% legit, you can do a Google search by yourself for:
isbn "978-3-8332-3835-2"
So, it turns out our three forum avatars actually depict Diablo 4 himself.
The last one is on the cover of “The Art of Diablo” book. So, if the 6 skulls signify the dead heroes from Diablo 3 (Necro can’t get more dead), would this mean we are getting new type of heroes or classless Diablo 4? Or they would be spirits in Heaven in D4?
EDIT: Here are some more screens from the book:
For more than twenty years, the artists behind Diablo have conjured new visions of the heavens and the hells, built nightmarish corridors filled with monsters and demons, and unleashed swarms of malevolent creatures upon tens of millions of players worldwide.
Featuring never before seen content, The Art of Diablo plunges into the concept, design, and environmental art that has defined the world of Sanctuary and the Eternal Conflict at the core of Blizzard Entertainment’s action-packed dungeon-crawling game.