Oda himself stated that inspiration for the Pirate climate in One Piece was from Vicky the Little Viking.
Further more many characters, arcs and other things in One Piece are based on some real life Pirates or other famous persons, incident, novels etc. Some of them include -->
---> Bartholomew Kuma
Edward Teach aka Blackbeard
---> Marshall D. Teach aka Blackbeard
and Eustace the Monk
---> Eustace Kidd
and Basil Ringrose ---> Basil Hawkins
(and his surname is probably referring to the Battle of Trafalgar
) ---> Trafalgar Law
Sir Francis Drake
---> X Drake
---> Scratchman Apoo
Alphonse "Al" Capone
---> Lafitte (Blackbeard Pirates)
--> Captain Morgan
--> Jesus Burgess (Blackbeard Pirates)
Zheng Zhilong (translation in japan means Tei Shiryu) ---> Shiryu of the Rain (Blackbeard Pirates)
---> Avalo Pizarro (Blackbeard Pirates)
Red Legs Greaves
Rudolph the Red-Nosed Reindeer
Michael Jackson ---> Jango
---> Jean Bart (Was formerly a slave and then joined Heart Pirates)
*Van Augur (Blackbeard Pirates) --> Van Augur bears a number of similarities to the character Adolphus from Terry Gilliam's film "The Adventures of Baron Munchausen". Adolphus is one of the eponymous Baron's henchmen, and has incredible eyesight and amazing shooting skills, able to detach an apple from a tree about 900 miles away. Van Augur's hat, glasses, hair, cape and rifle all contribute to this resemblance.
*Enel is based on Eminem (most of you must be knowing), an artist that Oda is fond of.
*Donflamingo is based on Jean Michel Polnareff. For some reason this artist is popular in Japan .
*Sentomaru is basically lifted from popular depictions of Kintaro.
* The three Admirals Kuzan (Aokiji), Sakazuki (Akainu), Borsilano (Kizaru) are basically based on Yusaku Matsuda
, Bunta Sugawara
and Kunie Tanaka
, all real life famous Japanese actors.
*Hogback from Thriller Bark --> Hogback is based on the Doctor Moro, who turned to genetically experimenting of animals to humans and on Frankenstain. Both of them were betrayed by their creations.
*Thriller Bark --> Oda is influenced by Tim Burton and his films some convincing example are Nin Gyoro and Bao, the servants of Moria very reminiscent of Lock Stock and Barrel on the homonym movie Nightmare before Christmas.
Nightmare before Christmas: Lock Stock and Barrel
Thriller Bark:Nin Gyoro and Bao
*Oars --> The zombie giant Oz is based in Óðr
, a god of Norse mythology.The name Óðr, which means "overwhelmed" is probably tied to the same root from which comes the name of the god Odin. In common with Oars is that, like all ancient gods of the vikings, he enjoyed fighting. The significance of his name, "overwhelmed" can indicate the shadow of Luffy who was inside.
and Château de Chambord
In Chambrod located in France have a common appearance.
*Crocodile is a mix of John Travolta and Steven Segal, both of who have achieved fame playing the opposing roles of Gangster and Cop
*Nico Robin, who worked with Crocilde, is based on Uma Thurman's character Mia Wallace. Travolta and Thurman both worked together in Pulp Fiction.
*Brook is obviously Jack Skellington, but there are also three famed musicians contributing to his look: Jimi Hendrix (Clothes+Fro) + Slash (Hat) + Ozzy Osbourne (Glasses).
Hope you find this interesting and a nice source of information. Would love if anyone has some more influences to share.