This is the Maw of Oblivion, created for Heaven's Fall back in the golden years of modding for me, when I loved every second of everything I was making and was still young enough to get away with spending all that time making it.
The model features a creature based on the Forgotten One, but with a purple skin texture overlay based on the Volcano's lava, as well as Forgotten One Tentacles that root into and out of the ground to form an alternate animation set where the Maw of Oblivion has retracted into his void portal.
Please do give credit to me on this one, but obviously as with almost all of my Warcraft 3 modeling work it is a derivative work of Blizzard Entertainment's original models, and so I believe you should be free to edit it without asking me -- just as I created these models without expressly asking Blizzard. Just please do give credit.
[Edit: The Hive's viewer cannot render it correctly, the portal and animated texture look different in-game.]