The orb of dominance is a mysterious object that comes from the end dimension, but its origins are unknown. The official Minecraft novel, "The End" mentions a god-like being called the Great Chaos. The Great Chaos was bored one day, and so it created the Ender Dragon. The Ender Dragon was like a pet for the Great Chaos, and eventually became the guardian of the main end island.
The Great Chaos is also dead set on destroying the overworld, and has sent many Ender Dragons to the overworld just to see them get defeated by the players.
Now we're gonna head back to the orb of dominance real quick. If you're familiar with the lore, you might've already noticed the similarities between the two. The orb of dominance slowly tempts it's prey with unimaginable power, then takes control of it's host. There are two examples of sentient beings being corrupted by the orb, and those are the Arch illager and the Wretched Wraith. The Arch illager becomes a giant creature made out of thick, black goo called the Heart of Ender. The Heart of Ender is very powerful, it can lead to constant laser attacks and a barrage of explosives. Though this might not be the orb's true form, it is quite powerful nonetheless.
The Heart of Ender has two more forms as a giant ender-centipede, and a centaur-pede (as stated by one of the devs). The Vengeful heart of ender could be the orb's true form, but something is missing. The Great Chaos is a god that can create new life forms in the end, and the orb's power is also drawn from the end. But if the two are connected, or the same being, the timeline breaks apart. It also doesn't make sense that the orb created the dragon, because there are many references to the Ender Dragon in dungeons.