Silvers Rayleigh, also known as the “Dark King”.

Rayleigh is a coating mechanic at the Sabaody Archipelago and he is also an expert in the coating business, as he performs such operations for various pirate ships heading down to Fish-Man Island, and he understands the workings of deep-sea currents.

Trivia

Silver is traditionally considered the next most valuable metal after gold, and as the first mate, Silvers Rayleigh was the second highest ranked man in the crew after the captain, Gold Roger.

Rayleigh appears to be left-handed. He has wielded his sword using his left hand on a few occasions.
Rayleigh is the first known character to have seen the Straw Hat worn by all 3 of its known owners.