Who is the "Man Marked by Flames"? The Key to the Last Road Poneglyph

The race for the One Piece has entered its final stage. Luffy, Shanks, and Blackbeard are all hunting for the same thing: The Fourth Road Poneglyph.

We know Big Mom had one, Kaido had one, and the Minks guarded one on Zou. But the location of the final red stone remains a mystery. According to Kid and Blackbeard, the only person who knows its location is a mysterious figure known as "The Man Marked by Flames" (or Hinokizu).

Who is he? And why is the World Government terrified of him?

What We Know So Far

The clues are scarce, but specific:

1. He sails a pitch-black ship.
2. He can create whirlpools to swallow enemy ships (suggesting a wind or water power, or powerful Haki).
3. He possesses the last Road Poneglyph (formerly located on Fish-Man Island).
4. He has burn marks on his body.

Theory #1 - Jaguar D. Saul

This is the most popular theory since the Egghead arc. We know Saul survived the Buster Call on Ohara and is currently hiding on Elbaf covered in bandages (burn marks from Aokiji's ice?).

• Why it fits: He is a Giant (Elbaf connection) and has been protecting the books of Ohara. It makes sense he would guard the Poneglyph too.
• The flaw: Does Saul sail a black ship? It seems he mostly stays on Elbaf.

Theory #2 - Monkey D. Dragon

The leader of the Revolutionaries has a distinct tattoo on his face (which could be interpreted as a mark/burn) and controls the wind (whirlpools).

• Why it fits: Dragon possesses the black ship Wind Granma. Holding a Poneglyph would prevent pirates from reaching Laugh Tale before the time is right.