Sanji is the chain-smoking chef of the Straw Hat Pirate Crew. He has superb fighting skills that only make use of his legs, in an effort to minimize damage to his hands which would impair his cooking skills.
Except a single fight where he uses knives against a fellow chef.
Sanji uses an array of powerful and varied kicking moves when he fights. His cooking skills are world class, and he was mentored in both cooking and fighting by Chef "Red Leg" Zeff of the Baratie. He was born in the North Blue, but grew up in the East Blue.
Sanji is trash-talking and serious, and usually gruff and impatient, especially around men. This is contrasted by his "love-cook" side, as he is very amorous around women. Sanji is completely devoted to any beautiful woman, usually losing all common sense and composure in front of them, then attempting to comically swoon them. This behavior has earned him the nickname "ero-cook," or perverted cook. He can also be very chivalrous and gentlemanly around women, volunteering to help them in various tasks and situations, whether they need help or not. He has sworn to never let insult or injury happen to any woman while he can still stand, even if that woman is trying to kill him. This is often problematic in his fighting as he can't attack female opponents, and would rather die than hurt them. All this is apparently the result of a "strict upbringing." To contradict his gentlemanly behavior, Sanji also enjoys seeing women wear skimpy clothing, and can be a voyeur.
His goal in life is to find the All Blue, a legendary ocean, which contains all the fish in the world. As such, it would be paradise for any cook with as much love for his work as Sanji, who holds great respect for the tools, ingredients, and art of cooking. So great is his devotion to his calling, that Sanji will not let any person or creature starve, regardless of them being friend or foe.
Being the crew's chef, he looks out for the health of his crewmates. Sanji respects Luffy as a captain, but often gets angry at him for eating too much, showing disrespect for the aesthetics of cooking, and generally being daft and irresponsible. He is constantly in petty fights with Zoro (sometimes calling him Marimo) over each others' traits and they have developed a rivalry, but have managed to make a devastating team together. He is very protective of the female crew members and Nami likes to take advantage of him, exploiting his extreme servility. Sanji originally wanted to cook Chopper, but has come to respect him as a crew member and friend. He's also good friends with Usopp; they team up and interact often, and Sanji understands him quite well. In short, he cares as much for the crew as any Straw Hat should, but unlike Zoro, Sanji shows these feelings more.
It is revealed that Sanji is the third son of the Vinsmokes, a family of killers. His father and one of the Yonkou, Big Mom, had arranged a marriage between him and the 35th daughter of the Charlotte family, Pudding during the strawhats time on Zoe/Dressrosa.