In the final battle, after the cataclysm had struck the Earth, after it was destroyed by Eaglemon, after Brondramon and Cobaldramon had devastated the Digital World. After Biodramon had contaminated what little peace was left. Even after the ultimate demise of Eaglemon, arose an old evil known as NeoDragoramon, who had killed every last human to exist. Everybody was powerless. The Royal Knights? Never existed in this continuity due to Eaglemon. The Olypmus Twelve? Also never existed for the same reasons. Any Digimon that stands between NeoDragoramon and total destruction of what remains of the very Digital World? The only opposition was the badly beaten Solomon, as what little he had left in his miserable existence had been swiftly taken from him by this new foe. Nothing seemed to exist as any hope for this world...
However, rising from the ashes of Solomon's shell as BlackWarGreymon, arose his own DigiCore, who denied any possibility of failing. He started off not even caring about his own allies, but after all he's been put through, all the hardships of his own existence, and how disastrous that NeoDragoramon's continued existence will be, Solomon's DigiCore is reconfigured by the Crest of Courage to change his attribute to Vaccine, and thus, allowed him to digivolve into his most powerful form, to the point NeoDragoramon stood in silence as he could not believe that BlackWarGreymon was capable of digivolving any further in this universe. He was proven wrong. Big time.
Arising from his future grave, is the first, and last, of the Royal Knights to exist in this continuity. Solomon died as BlackWarGreymon, but his battle was not over. As the only individual of his species, he is technically known as DeusGreymon, derived from the Latin term "Deus" (Deus: God). However, Solomon chose not to use this name, and instead believed he was his own being, and defined this new form as his own name (Solomon). He is given the title of "The Last Deity", since aside from NeoDragoramon, he is the only Digimon still alive in a dying world. As the final battle ensues, Solomon destroyed his adversary using various energy weapons that he had the ability to summon with his hands, transforming both of his arms into any type of weapon to exist. After a long battle, Solomon recreated the Human and Digital World in which he and Eaglemon never existed, and that there was never a link between either world. However, to say he would go unremembered is a mistake, as Solomon is reborn into the Digital World as Botamon, alongside his former allies who had perished in the final battle.
Digimon Classic[]
Everything that is described above, essentially, as this is the only planned appearance of DeusGreymon. In all cases, the species is known as Solomon, since it is the final form of it's namesake, Solomon. DeusGreymon's existence was barely known about, since up until him acquiring this form, the species itself did not exist; Had any other BlackWarGreymon tried to digivolve further with the Crest of Courage beforehand, it would not have worked. Solomon only becomes his final form upon realizing that he finally does want to be more than what he was created as, and much more like what Taro had told him about other Digimon universes, especially the Royal Knights. Hence, he gave up his Virus Attribute to allow himself to become this final form, as he slays NeoDragoramon permanently with his new found powers.
In terms of his physical appearance, Solomon himself apparently had part of how he looked in this form, as his mind focused with the intention of Digivolving into Omnimon one day, hence why this form partially resembles bits and pieces of Omnimon and Alphamon. Another note to point out is that, like NeoDragoramon, their exact power levels will never be able to be determined. True, they both are meant to be equals in terms of power, but when compared to other powerful Digimon, nobody can truly say whether or not these two are the most powerful. However, for references sake, in the Digimon Classic continuity, they both are tied for the most powerful Digimon.