I see in the terms of service it says: "Posting of commercial images/links is limited to active vendors and products in the Renderosity Marketplace."

However, I don't see anything that says you can't post the name of an artist or site. So, on that basis, I will say those pictures appear to be of the Terra-Titan by Summoner, available on the site Freedom of Art.

It looks like there's some great work there (although I haven't tried any of it). It doesn't look like any of it has superfly materials, so the renders don't have the same sense of realism as what the OP posted. On the other hand, just converting the shaders seems a heck of a lot easier than starting from scratch and creating an all new figure. Also, if you felt like selling materials for a model like that, I've seen plenty of vendors include links to required products on other sites when selling such add-ons.