Iwa Doctor

He was a doctor who worked with the retired Third Tsuchikage Ōnoki, to create the Fabrications and Akuta.

Background
At some point after the Fourth Shinobi World War, the doctor had acquired the genetic material from the White Zetsu. One day, he approached Ōnoki, whose hopes to create artificial soldiers to replace the shinobi of Iwagakure backfired, to offer his services with the material he obtained. With it, they created the Fabrications, artificial humans to help lead the Akuta, mindless soldiers created from clay. To lead the Fabrications themselves, the doctor and Ōnoki create a Fabrication clone of the Tsuchikage himself, Kū.

Personality
The doctor was loyal to Iwagakure's well-being that he was willing to assist the Third Tsuchikage in creating a private army that undermines the peace treaty of the Shinobi Union. However, unlike Ōnoki, the doctor was willing to commit sacrifices to ensure these soldiers will have a stable body to serve their duties.

Abilities
The doctor was very intelligent, being able to use the genetic materials acquired from White Zetsu to create artificial lifeforms, the Fabrications, and even integrate them with certain genetic anomalies to grant them advanced nature transformations.

The doctor's scientific ingenuity did have its limitations, as his creations were flawed with unstably short lifespans and durability. He managed to overcome this flaw by examining Mitsuki, a different type of artificial human (limited by a cursed seal that he cannot get through), though it requires a human to be sacrificed in the process, which defeats the very purpose of having Fabrications to protect humanity to begin with.

Mitsuki's Disappearance Arc
The doctor assisted Ōnoki in maintaining the Fabrications' fragile health, and seeking a method to stabilise them permanently. Upon bringing in Mitsuki, the doctor did an examination on the artificial boy's body. Though Mitsuki's heart had a cursed seal blocking the sensors from learning the body's secrets in-depth, the doctor was able conclude that he can craft an artificial heart by using a live human's heart as raw material, which can be used to extend a Fabrication's lifespan.

Though Kū was at first reluctant in trampling over Ōnoki's creed, he eventually had Iwagakure under lock-down and ordered the doctor to proceed in creating artificial hearts for all the Fabrications. However, before the doctor could extract the raw material out of five Iwa-nin, the Fourth Tsuchikage was freed from imprisonment and led a counterattack against Kū's faction, freeing the "donors" who in turn bound the doctor as they left to deal with the Akuta.

When Kū returned to the lab, fatally wounded by Mitsuki, he released the doctor to have him prepare the artificial heart. The doctor notified him due to the donors' escape, the heart remains incomplete. Kū, noticing that all that is required to complete his new artificial organ is a human heart, turned around to kill the doctor for it, who was overwhelmed with horror as the Fabrication attacked.

After Kū was killed by Ōnoki and Iwagakure was back in the custody of Kurotsuchi, the Iwa-nin found the doctor's corpse was gone. Orochimaru and Log later noted that someone was probably interested in the doctor's ability to create such powerful artificial lifeforms.

Trivia

 * It is implied that due to the disappearance of his corpse and his research gone missing, that the doctor could have had connections to Kara.