Sanji (サンジ, Sanji), born as Vinsmoke Sanji (ヴィンスモーク・サンジ, Vinsumōku Sanji) and also known as "Black Leg" Sanji (黒足のサンジ, Kuro Ashi no Sanji), is a fictional character in the One Piece franchise created by Eiichiro Oda. The character made his first appearance in the 43rd chapter of the series, which was first published in Japan in Shueisha's Weekly Shōnen Jump magazine on June 8, 1998. He is the fifth member of the Straw Hat Pirates and the fourth to join, serving as their cook.

A native to the North Blue, Sanji grew up as part of the Vinsmoke family under his father Vinsmoke Judge, king of the fallen Germa Kingdom, and mother Vinsmoke Sora. After leaving his abusive family and surviving a shipwreck, almost starving to death on a rock, he was taken under the wing of "Red Foot" Zeff, a former pirate and owner of the floating restaurant Baratie who taught him cooking and his fighting style, which is characterized by the use of legs in combat, leaving his hands for cooking. Following a battle against Don Krieg, Sanji joins the Straw Hats in order to fulfill his dream of finding the All Blue, a mythical sea said to have fish from around the world. Despite his calm and rational nature, he is known for his constantly enamored behavior around beautiful women (especially Nami), to the point he refuses to attack women to the crew's and his own detriment.

Early designs show that, originally, Sanji was going to be a gun-wielding black-haired character named Naruto but that idea was scrapped.

Oda was inspired by Mr. Pink, Steve Buscemi's character in Reservoir Dogs (1992), when creating Sanji.

Sanji is a tall, light-skinned, slender man who has a small waist. He commonly wears a black shirt and smokes a cigarette. Before the timeskip, Sanji is seen with his blonde hair covering his left eye. However, after the timeskip, his hair covers his right eye. Before leaving his family, Sanji styled his hair in the opposite direction and wore a yellow shirt with a black number three on it. He also wore white pants, brown boots, and a yellow bandana. After leaving his family and still a child, he started wearing a white cook's uniform. Sanji grows a goatee during the timeskip, and concept art shows this was his original design.

Sanji's most distinctive feature is his eyebrows, which are characterized as swirls with the tail end pointing at his left side, opposite in direction in comparison to his siblings Ichiji, Niji, Yonji, and Reiju.

Oda revealed Sanji's real-world nationality would be a Frenchman, in contrast to the Nazi Germany themes of Germa 66.

Sanji is mostly seen as a composed, nonchalant, and calm individual who always keeps his cool when in dire situations. However, this is contrasted by the many comedic gags he partakes in, such as when in the presence of a lady or when insulted by a crew member. Most notably, Sanji and Zoro have a great rivalry, often resorting to fighting (both verbally and physically).