Rayleigh is a fun loving and care free, not unlike Monkey D. Luffy and Gol D. Roger, his former Captain. In the his past as First Mate to Gol D. Roger he was serious and strict in matters of crew discipline. He is open and talkative, except when it comes to the mysterious Black or Void Century, however he was willing to tell Nico Robin if she wished, but she declined his offer.
Although former rivals, he and Whitebeard talked about the past nostalgically, he also has great respect for him, as seen when he passed.
Rayleigh is apparently extremely powerful, possibly one of the strongest characters introduced in One Piece, he has huge stamina as shown when he killed several giant Sea Kings acreatures that rules the seas in One Piece, while swimming to Amazon Lily to see Luffy, from across the ocean, even though he said is 'getting old'. Rayleigh is around Whitebeard's age (72 before death).
His partner in business Shakky, said that he is '100 times more powerful then all of you boys', in reference to the Eleven Supernovas.
He works as a Coating Mechanic , which allows ships to travel underwater to Fish-men island and act as submarines in general (as seen on Whitebeard's ship during the battle at Marinford ). He uses the coating Yaruikiman resin, he is also said to be one of the best.
Weapons: He is skilled with a sword, although he self proclaimed that he is out of practice. Though he did stalemate Kizaru, the fastest of the Admirals.
He is an experienced and talented user of Haki, an ability of the spirit and willpower that can allow you to overcome a Logia devil fruit users powers ( which includes intangibility if desired) ,along with his phenomenal strength he is more then formidable. He is even able to match Admiral Kizaru in battle, and even wound him His Haki can be focused, he took out an entire room with it, except the Straw Hats and Keimi and his crew mate.
Strength: class 100