During the era when the Rocks Pirates were active, he was the overlord of the seas who overpowered Rocks, known as the Black Dragon King.
At God Valley, Rocks is defeated by Garp and Roger, but Rog overpowers them both and single-handedly storms the heart of the Holy Land. Due to a System error, however, he falls into a seal.
In the year 1492 of the Sea Circle Calendar, he awakens from the seal and happens upon Kaido. With overwhelming strength, he defeats him and makes him his underling.
Doflamingo: "Fufufufu! No one can withstand his power. Be afraid, tremble! He'll turn the world controlled by you Celestial Dragons upside down!"
Kaido: "They call me the Strongest Creature on land, sea, and air? No, no. My big brother, the Black Dragon King Rog, is the real Strongest Creature on land, sea, and air."
Bullet: "Rog, because it's you, I'm willing to give it everything I've got. I'll be the one to defeat you!"
Whitebeard: "Though it pains me to admit it, I have to acknowledge that Rog possesses a power the world has never seen before..."
This novel and its characters are entirely fictional. Any resemblance to actual people or events is purely coincidental. Do not imitate.
There's someone up there, it's only a few pages
Is this a period before the Yonko?