DAZ3d is or at least was a subsidiary of Zygote, which supplied Poser with it's first figures all the way up to Poser 4. DAZ3d split from Zygote and started an online store that made and brokered 3D content primarily for the Poser community.

About 4-5 years ago, Poser's continued existence was in doubt (I forget exactly why, but I think it had something to do with Poser being sold yet again to e-Frontier). DAZ3D decided to hedge it's bets and began to create it's own 3D application, DAZ Studio.