Zephyr was responsible for training many future Marine heroes which included the likes of Akainu, Aokiji, Kizaru, Onigumo, and Momonga. Zephyr did not possess any devil fruit, but he was very apt at using Haki.
Zephyr: Zephyr was Kizaru's mentor a long time ago before he defected the Marines.
Borsalino, more commonly known by his alias Kizaru, is an admiral in the Marines. After Aokiji resigned from the Marines and Akainu was promoted to fleet admiral, Kizaru is now the only remaining admiral from the previous trio.
Kizaru is likely One Piece's weakest Admiral seen thus far. Despite having the strongest Fruit on paper of the five Admirals seen, he never utilizes it to its fullest potential. While still an Admiral and therefore incredibly strong, he's most definitely the weakest of the bunch.
When Aokiji joined the navy he was called the recruited monster and possessed a great fighting force that he had not learned from anyone, but he gained more strength when Monkey D Garp trained him.
Garp is easily the most powerful Vice Admiral in the Marines, and rivals or exceeds the power of the known Admirals and Fleet Admirals. After then-Admiral and future Fleet Admiral Sakazuki (also known as Akainu) killed Ace, Fleet Admiral Sengoku held Garp down to prevent him from killing Sakazuki in revenge.
Saving Ace would have gone against Garp's loyalty to the Marines. After all, Ace was not just any pirate; he was the son of the Pirate King Gol D. Roger himself, and his execution was seen as a crucial step in the fight against piracy.
Currently, Ryokugyu, Fujitora, and Kizaru are the three Admirals of the Marines in One Piece.
Going by the beast and deadly nature of Kaido, who was dubbed the strongest creature in the world of One Piece, Admirals such as Kizaru would almost certainly struggle against Luffy who defeated Kaido.
Marco, also known as 'Marco The Phoenix', is the former right-hand man of Whitebeard, and one of the most fearsome pirates in One Piece. He possesses the Mythical Zoan Phoenix fruit, which is considered to be even rarer than a Logia. At Marineford, Marco proved his worth by fighting against all three of the Admirals.
Vegapunk's Light-Pressure Gloves Can Beat Kizaru
Because Kizaru's Devil Fruit is a Logia type, he is able to completely turn into the element associated with it, which in his case, is light.
Aokiji is a powerful member of the Blackbeard pirates and here's how he joined them. Kuzan is a very memorable character in One Piece who was introduced to the fans before the 2-year timeskip for the very first time. Making his debut during the Water Seven saga, Kuzan was revealed to be an Admiral of the Navy.
Kizaru is a very laid-back, easygoing and lazy invidual. He speaks in a very slow manner and often drags his syllables out. He also seems to be irresponsible regarding his own strength, as he non-chalantly destroyed a mangrove tree on Sabaody Archipelago, something that he wasn't supposed to do.
During their fight, Rayleigh was also able to cut Kizaru, which created a small wound. The altercation between the two clearly indicated that Rayleigh is stronger than Kizaru.
Kizaru was a fairly prominent figure in the Murder Game, due to being a traitor. He tried his best to stay in the game but in the end got voted out by a technicality.
Well, the answer is simply because he doesn't want to have anything to do with the Celestial Dragons. After all, Admirals of the Marine have to answer directly to the Celestial Dragons, and have to quickly come to their aid whenever they encounter a problem.
Sengoku the Buddha was the former Fleet Admiral of the Marines. He became monstrously powerful after he ate the Hito Hito no Mi, Model: Daibutsu, and a colossal Zoan-type devil fruit. He was the ultimate powerhouse. Sengoku is the only Marine who possesses all three powers of Haki.
Yamato was capable of holding back Kaido and that's all an Admiral has to do. Kid and Law took down Linlin, two Admirals would decimate her. Once that happens, Three Admirals at the same time vs Kaido would destroy him in a minute. Admirals also has greater teamwork than two yonko.
Being admirals, the three are capable of using Haki and showed themselves to be extremely proficient when using advanced Busoshoku Haki together to block Whitebeard's powerful shock wave.
While in this form, Sengoku can unleash enormous shockwaves. Normally with such a powerful devil fruit, the user would best anyone in a fight, but Garp's insane haki makes up for his lack of devil fruit. The fight between the two legendary Marines would be close, but Garp would come out on top almost every time.
Garp bears a grudge against Shanks, because Garp believes he is the one who influenced his grandson, Monkey D. Luffy, to become a pirate.
Even though Garp didnt do anything physically he shows is support by letting Luffy hit him put of the way. That was Garp's way of saying save Ace.