Silvers Rayleigh is a legendary figure from the era before the Great Age of Pirates in the World of One Piece. Known to be the right arm of the Pirate King, Rayleigh was the Vice Captain of the Roger Pirates. He is held in legendary light in the world of One Piece and remains to be one of the very few people alive who know about the true history of the world.
In terms of combat, Rayleigh is a tremendous fighter and came to be feared as the Dark King during his time as an active pirate. Currently, Rayleigh is an old man and is quite past his prime, however, he is still feared, as seen in One Piece 1059, where he made Blackbeard retreat from Amazon Lily. With great Haki and incredible sword skills, Rayleigh is still a threat to be feared in the One Piece world.
Rayleigh's Haki
Rayleigh is one of the few people in the world of One Piece who belong to the top tier yet do not possess a Devil Fruit power. As fans know, he, along with a few other members of the Roger Pirates, did not possess any Devil Fruit ability. In Wano, Kaido made it quite clear that Haki is an ability that transcends all. As such, it is arguably the strongest of all the powers in the One Piece world. Rayleigh being a master of this ability made him feared all across the world. As already made evident during his introduction, Rayleigh is a user of all three types of Haki.
His Color of Observation is certainly quite special, evident from when he began training Luffy on Ruskaina. At the same time, Rayleigh demonstrated the usage of the Color of Armament when fighting Kizaru on Sabaody Archipelago. He also showcased his ability to use Conqueror's Haki on various occasions, the most notable one being when he introduced himself to Luffy. Being an elite fighter in the One Piece world, it is no surprise that Rayleigh can also coat himself and Conqueror's Haki. In the recent chapter, he was shown making use of Conqueror's Haki coating while confronting Blackbeard. As such, Rayleigh is truly an incredible user of haki.
Rayleigh's Portrayal In Prime
As the right-hand man of the Pirate King, Roger, Rayleigh is known to have been extremely powerful in his prime. According to Garp, even in his old age, he is an incredibly dangerous individual, and capturing him during the Sabaody Archipelago arc would've taken a lot of preparation. His pedigree was compared by Garp directly to Whitebeard, which just goes to show that he is a monster even in his old age. In his prime days, Rayleigh was certainly several times stronger than he is at the moment, it wouldn't be a stretch to say that his strength would be comparable to that of the Yonko of the One Piece world.
In the previous chapter, Rayleigh mentioned that he wouldn't be able to defeat Blackbeard due to his old age, implying that had he been in his prime, he would have been a match for the Yonko despite him having two and possessing powerful Haki. His epithet of the Dark King implies that he is someone comparable to Roger in certain ways. Well really wouldn't be equal to him in terms of power, he would certainly have to be close for him to attain such a special moniker.
Rayleigh's Strength In Old Age
In his old age, Rayleigh is clearly not as powerful as he once was. This was evident from his class against Kizaru when the two met during the Sabaody Archipelago arc. Despite being able to stop him successfully, Rayleigh was getting tired rather quickly due to his body not being able to keep up as well as it could have once. Nonetheless, he was fairly certain about holding Kizaru off and even defeating him had the need arisen. In One Piece 1059, he went on to confront Blackbeard on Amazon Lily. His pedigree was such that the Yonko retreated immediately from the island.
However, later, Rayleigh clarified that it was only his reputation that saved the day. Har confronted Blackbeard in a full-on battle, he would have lost due to having grown old. This certainly implies that he is far from his strongest self. Nonetheless, he is still a user of Conqueror's coating and other powerful forms of Haki. His swordplay is still quite immense. While not nearly as strong as the Yonko, he is certainly someone who can give any Yonko a run for their money. After all, he is still a legend and fans saw in the Marineford arc what a legend can do despite their worsening health when Whitebeard took on the entire Navy by himself.