Void gods are the most powerful type of voidwalker yet encountered. They are gigantic and, unlike void lords, wear no armor. The first, encountered by adventurers in the Sunwell, was born from a dying naaru named M'uru, and some parts of the naaru's form are still visible. A second was born of the alternate timeline's K'ure, a transformation which was initiated by Cho'gall deep within Oshu'gun on Draenor.
However, these two are not confirmed to have been born of a dying Naaru, so it is debatable as to whether these are actually Void Gods, or another class of powerful void being which happens to use the same model.
Ner'zhul summons this creature using powers drawn from The Dark Star during the quest  Shadows Awaken. Again, this being is not summoned as a result of the death of a Naaru, but rather the leeching of it's energies while it is still in it's darkened state. It is also referred to as only a shard/fraction of the Dark Star's power, so it's classification is unconfirmed.