Too many to list. Oda takes a lot of inspiration from a lot of things, like Hindu mythology. Luffy is based on the Monkey God Hanuman. Hanuman is also known as Bajrang Bali, which is a reference to Luffy's Bajrang Gun attack. Then you have other references, like how Imu seems to be a reference to Vritra, the personification of evil and drought who is the leader of the Asuras. There are noticeable similarities, like how the WG rules the seas (Vritra controlled all the water of the world) and how the WG hides the existence of the Sun God Nika (Vitra once hid the sun).
Other personal favorites of mine involve Blackbeard, Brook, and Vegapunk. For Blackbeard, his first name (Teach) comes from the last name for the real life version. Whitebeard's last name (Edward) was also the real life Blackbeard's first name. Thatch was an alias used by the real Blackbeard sometimes. By killing them both, stealing the DF found by Thatch, and absorbing WB's powers, Blackbeard has truly become... Blackbeard.
Brook has a few I find interesting:
- Brook's age (88) and height prior to the timeskip (8'8") is a reference to the number of keys on a piano (88)
- Brook's laugh ("Yoho") is a common pirate stereotype originating from "Dead Man's Chest", the sea shanty from the book Treasure Island
- Brook's birthday, April 3, comes from his Devil Fruit's name since 4-3 can be derived from yo-mi
Dr. Vegapunk has quite a bit. His original body is a homage to Albert Einstein, especially the famous photograph of him sticking his tongue out. The apple on his head seems to be a reference to the story of the Sir Isaac Newton developing his theory on gravity after an apple fell on his head. Interestingly, several of Vegapunk satellites share a mythological connection with the moon too. A Lilith Moon denotes a dark moon, whereas a Shaka Moon denotes a full moon. The former is named after an evil, mischievous figure of Judaic mythology while the latter is named after the person who became the Gautama Buddha after reaching enlightenment, which fits both of their personalities. Also, while Edison and Pythagoras are both named after the famous and highly influential inventor and mathematician, which fits with the technology setting, they also happen to be craters on the moon; ditto for Atlas. As for the original Vegapunk, he is the sun, the "Stelle" or star, since in Japanese the word "star" can refer to either a planet or a star. It remains to be seen if this has any deeper connection with the lunar city Birka or if this is simply a reference to the science and futuristic association of space, as if Vegapunk already reached beyond space and the stars.
Dr. Vegapunk's design is also a homage to various manga characters. Atlas is clearly inspired by Astro Boy. Atlas is the name of the evil rival of Astro Boy in the
Astro Boy series who has high combat power. There are also traits from Nagato from
Naruto. Nagato is an engineering genius, hails from a highly industrialized country, and has the ability to replicate people's special abilities. Like how Nagato was crippled and forced to invent proxies for himself, the original Vegapunk may have been left crippled by Caesar when he unleashed that nuke during a flashback that occurred during the Punk Hazard arc. And like how Nagato can replicate jutsu, Vegapunk is the only person in the manga thus far who has shown the ability to replicate DFs. I got the impression of Francoise Arnoul (Cyborg #003) from
Cyborg 009 when I saw York's design.
The sheer amount of detail that Oda crams into each and every chapter is mind boggling to behold. You have Dragon and his symbolism of the Cuban Revolution, Ivankov's prisoner number in Impel Down being 6582, which is the scientific gene identification number (Gene ID) for
Homo sapiens, Doflamingo being a reference to Don Quixote, the main character of the famous Spanish novel "
El ingenioso hidalgo don Quijote de la Mancha", and Gecko Moria being a possible reference to Dr. Moreau from the novel "
The Island of Dr. Moreau". Ad infinitum.
