For starters, Volthoom seems to have been retconned into the proverbial 'Hand of Creation' which was responsible for spawning the DCU-proper...
Volthoom first appeared right after the Guardians originally witnessed the 'Hand of Creation'... But upon closer inspection, they noticed that it was wearing a GL ring:
http://i.imgur.com/x85f4Gv.jpg
*Note the GL ring on the middle finger of a right hand.
Full scene:
http://i.imgur.com/cOpIggY.jpg
http://i.imgur.com/dMp3DG7.jpg
http://i.imgur.com/lVeoFO4.jpg
In a nutshell: the Guardians witnessed the Hand birthing creation, noted a GL ring on the Hand, their instrumentation inextricably shattered, and *poof* Volthoom(in his original/human form) arrived. He then taught the Guardians of the emotional spectrum and convinced them to purge ALL of their emotions -- thereby creating the First Lantern/Ring(and empowering himself) by proxy:
http://i.imgur.com/0w07Crs.jpg
http://i.imgur.com/9ZwPru3.jpg
Coincidence? Hardly.
We later learned that peak Volthoom had harnessed the power of the emotional spectrum with the intent of "unwinding the fabric of history" for his own purposes:
http://i.imgur.com/c2ciIoU.jpg
Volthoom then literally pulled the first(and most powerful) GL ring from inside of Ganthet:
http://i.imgur.com/o19k08w.jpg
*Note that he places it on the middle finger of his right hand.
This panel makes it clearer to see the ring placement:
http://i.imgur.com/SPwbVkn.jpg
*Again: Middle finger. Right hand.
Why is this important? Because when he used Hal as a focal point, Volthoom began unraveling ALL history, starting at the beginning... He became the Hand of Creation:
http://i.imgur.com/6yWuov8.jpg
*Note the GL ring on the middle finger of his right hand.
Full scene:
http://i.imgur.com/Bawjtq8.jpg
http://i.imgur.com/HHXgPoY.jpg
How do I know Volthoom was *actually* collapsing/altering the timestream? Because WL Kyle could literally feel it happening:
http://i.imgur.com/lAG22w1.jpg
The 'retconned' Hand was featured again in a completely different arc, and described as the force that originally spawned the multiverse, as well as the Old(and New) Gods:
http://i.imgur.com/Kz8n3fd.jpg
*Note a ring on the middle finger of a right hand.
Full scene:
http://i.imgur.com/OvgYg3k.jpg
http://i.imgur.com/cQGHFHq.jpg
Moreover, Volthoom stated that he had already traveled to the beginning of time and witnessed his destiny:
http://i.imgur.com/7BxVwcE.jpg
So it is not only my opinion that Volthoom has been retconned into, essentially, the force responsible for birthing the DCU -- but he may have also sent his original/human-self back in time, in order to perpetually repeat the process of his transformation. Essentially, he was/is his own creator.
tl;dr
At full power, Volthoom is a Supreme Being-esque entity.
