Indigo

 Dr. Indigo (Dr. インディゴ) is an ingenious member of Shiki's crew. He is the one that created Boss and the other monstrous animals under Shiki's dominion.

Appearance
Indigo is a huge man with a mime-like appearance. He has indigo hair, with two particularly large tuffs at the side of the head, and his face is white, with purple lines near his eyes, presumably some sort of make-up. He is pot bellied, with thin limbs, and a muscular torso. On his forehead he has a pair of purple round-shaped eyeglasses. He wears a large yellow polka dotted indigo scarf and indigo-striped shoes (similar to Kuro's) that make a farting noise every time he takes a step. He also wears indigo overalls, with two lines of bottons on the front, and a lab coat over them. On his hands there is a pair of brown gloves.

Personality
Indigo is a doctor with an eccentric personality: he has a distinct laugh which goes "Piro piro piro", adorns shoes that emit sounds of flatulence whenever walking, doesn't caring if others gets irritated by this, and also often tries to act like a mime, but usually breaks character by suddenly talking, though ironically becomes completely surprised if someone actually understood his charade type speech. He also appears to be prudent, as he always carries around a phial of antidote to the Draft disease, just for precaution.

Shiki
Indigo shares a rather humorous relationship with his captain Shiki. Whenever Shiki says or does something stupid, Indigo acts as a straight man and slaps him, after which they both present themselves to others like a typical comedy duo after a joke. He also has an habit of trying to explain something to Shiki through odd movements and gestures until Shiki tells him to just come out and say it (though at one point in the movie, Shiki understood what he was trying to say much to Indigo's surprise). Regardless, he is loyal to Shiki and spent twenty years creating super-powered creatures in Merveille for the Golden Lion Pirates to take over the world. He also plays a part in Shiki's dances, along with Scarlet.

Abilities and Powers
Indigo is a terrific chemist. He was the one in charge in the development of Shiki's scheme involving all the monstrous animals, and was the one who developed the SIQ serum. He may be a strong fighter who uses scientific materials since he was seen along Shiki and his crew when they fought against Gol D. Roger and his crew. He's possibly a skilled swordsman, as he was seen attacking Luffy with a sword fitting his size, and wielding it during the battle in Shiki's palace.

Indigo is also a skilled dancer, taking part in all of his captain's little "dance shows".

Chemical Juggling
He has the ability to produce explosive chemicals from his body and attack with them, called Chemical Juggling. He uses his ability to create chemical orbs, that are then arranged above him and shot from his hands, causing explosions. He can also create a larger orb with a far more explosive effect, which he calls Mass Juggling. The way he manipulates the chemicals resembles to the skill of Juggling. It is unknown if this ability stems from a Devil Fruit or from some sort of chemical he used on himself.

Battle in the Edd War and afterwards
Indigo was at Shiki's side during the Battle in the Edd War, where the Golden Lion Pirates confronted the Jolly Roger Pirates. After the battle, he was seen at his captain's bedside, commenting on his positive attitude towards the steering wheel stuck in his head. He then slapped him in a comedic fashion for mistaking himself with a rooster.

It's unknown what happened to Indigo during the two years Shiki spent in Impel Down, however when Golden Lion broke free of the gaol and reached Merveille, the loyal scientist was one more time at his side, ready to start developing an ambitious project to defeat the World Government.

2| Pre-Movie Arc: Little East Blue
Shiki was briefly seen during the Little East Blue Arc, commenting on Boss having escaped from him, and then reassuring his captain of the plan's guaranteed success.

Movie 10: Strong World
Indigo was first seen dancing before Nami with Shiki and Scarlet, in the palace's greenhouse. He proudly showed his captain the new development, a bird producing electricity from his feathers, who ended up shocking the three pirates. He spent the major part of the film at his captain's side, miming the most important news before telling him and the onlookers openly; he was quite surprised when Shiki managed to understand the news regarding Nami's attempt to blow up the Daft Green trees just trough his miming actions.

Once 20 years have passed, Shiki put his plan into action. This involded having Indigo enhance the chemical I.Q (which was produced from the Daft Green) into a stronger form which Indigo dubbed the SIQ that, when injected into the animals, would cause them to mutate into bigger forms with increased strength, intelligence and aggression. Shiki would then send the animals down to East Blue and have it destroy villages till he would eventually conquer the peaceful sea. However their plans are brought to a halt when the Straw Hats interfere on the night they were to commence the operation, having earlier gained their ire by kidnapping Nami. Indigo tries to stop Luffy from going after Shiki but Zoro gets in his way.

Later Chopper and Ussop manage to find Nami but finds she has been infected due to overexposure to the Draft Green plants and go to find a cure. They wind up running into Indigo who has such but refuses to hand it over. Zoro soon arrives and proceed to battle the doctor. Despite Indigo's best efforts he ultimately beaten by the swordsman. He later seen falling into the ocean with Scarlet after Shiki is beaten and his control over the floating islands is broken.

Trivia

 * Of Shiki's main crew members, they all have a color in their name.
 * The reason his scarf is always hovering behind him (as if wind was blowing through it) is because there is a wire inside the scarf.
 * Indigo shares many distinctive traits with the character Mayuri Kurotsuchi from the series Bleach: they're both scientists with eccentric personalities, blue hair, seemingly painted faces and using particular abilities related to chemicals. Also, in the original Japanese version, they have the same voice actor.