The Ba'ku were a humanoid species who lived in a single village on the planet Ba'ku inside the Briar Patch, in Sector 441. In 2375, they had a population of 600. Due to the life-giving properties of their home planet, the Ba'ku became embroiled in a conspiracy between Starfleet and the Son'a. (Star Trek: Insurrection)
The Ba'ku originated from a technologically advanced civilization with knowledge of warp drive and positronic devices, who once explored the galaxy. In the early 21st century, their race verged on self-annihilation due to the development of weapons of mass destruction.
In 2066, a small group of dissidents fled their star system and settled on a planet inside the Briar Patch, where they would be isolated from the threats of other worlds. Now called the Ba'ku, they discovered that an unusual metaphasic radiation emanating from the planet's rings granted them effective immortality. The Ba'ku abandoned their technology and adopted a slower pace of life.
In the mid-23rd century, a band of young Ba'ku rejected the simple lifestyle of their elders. Led by Ro'tin and Gal'na, they unsuccessfully attempted to seize control of the settlement. The rebels were subsequently exiled from the planet and became the Son'a, a nomadic spacefaring power. The Son'a never forgave the Ba'ku for depriving them of their immortality, and were determined to one day return and take the metaphasic radiation for themselves.
By 2375, the Briar Patch lay within Federation space. Ro'tin, now Ahdar Ru'afo of the Son'a, offered to collaborate with Admiral Dougherty of Starfleet to harvest the metaphasic particles from the Ba'ku planet using a Son'a collector. As the process would render the planet uninhabitable, a cloaked Federation holoship would relocate the Ba'ku unknowingly to another world. As Starfleet believed the Ba'ku to be a pre-warp society, they built a duck blind on the surface and used isolation suits for cultural observation.
After being damaged by a Son'a, Lieutenant Commander Data exposed the duck blind, telling the Ba'ku that Starfleet and the Son'a were their enemies. The USS Enterprise-E arrived to assist and discovered the holoship. Dougherty claimed that, as the Ba'ku were not indigenous to the planet, the Prime Directive did not apply and the relocation was justified by the immense medical benefits the metaphasic radiation would give the Federation. Captain Jean-Luc Picard countered that removing the Ba'ku against their will was fundamentally immoral and a betrayal of Federation principles.
Picard and several Enterprise senior staff members transported to the planet to protect the Ba'ku, while Commander William T. Riker raced the Enterprise away to inform the Federation Council of the conflict. Losing patience, Ru'afo ordered the Ba'ku to be taken by force and when that failed, murdered Dougherty and initiated the metaphasic collection process irrespective of those still remaining on the surface. Enterprise personnel managed to destroy the collector, defeat the Son'a forces, and take control of Ru'afo's flagship.
In the aftermath, the Federation Council halted the Ba'ku relocation plans pending a top-level review. Several Son'a, including Subahdar Gallatin, rejoined their families to live in peace. (Star Trek: Insurrection)
The Ba'ku resembled Humans in appearance. The metaphasic radiation from their planet's rings continually regenerated their genetic structures, which stopped them from aging once they reached maturity, conferred perfect health, and prevented permanent illness or injury. From a young age, the Ba'ku developed remarkable mental discipline and clarity of perception. After centuries, some even learned to slow down the passage of time in a local area, allowing them to explore the depths of a single moment. (Star Trek: Insurrection)
The Ba'ku were a community-oriented, pacifistic agrarian society. They employed only simple machines, asserting that technology diminished those who took advantage of it. They refused to use weapons, even in self-defense, believing that to do so would be to lose everything that they were. Young Ba'ku artisans apprenticed for several decades to develop their skills. (Star Trek: Insurrection)
The Ba'ku were originally going to have a spotted-pattern makeup along the sides of their face to differentiate them from Humans, with forty different designs considered. With two hundred extras in physically active scenes over weeks of filming, time and budget nixed the idea. Makeup Assistant Bradley M. Look also noted that there were production concerns the design would not be clearly distinguishable from Trill characters in the film. (The Secrets of Star Trek Insurrection, p. 58.)
Instead, Costume Designer Sanja Milkovic Hays was charged with developing clothing that would sufficiently make the Ba'ku seem alien, by using only natural fibers, a custom cellulose fabric, and avoiding leather, "because they're a nonviolent society." (The Secrets of Star Trek Insurrection, p. 58.) The colors the Ba'ku used were intended to be strictly derived from nature, vegetables, flowers, and fruit. (Star Trek: Costumes, p. 164)
According to the novelization of Star Trek: Insurrection, the ancestors of the Ba'ku were called the Ka'bu (the pacifistic dissenters made a linguistic play on the name by reversing the consonants to call themselves the Ba'ku, meaning "the Peaceful"). The Ka'bu had traveled the galaxy in sophisticated space vessels and lived elegantly in the pursuit of beauty, art, and physical perfection, relying on mechanization to do their labor for them. However, the artist class had separated from the warrior class, and it was squabbling between the classes that caused their downfall, not the availability of weapons.
According to the RPG sourcebook Planets of the UFP, the ancestors of the Ba'ku were called the Brek'a. In 2066, a group of 500 Brek'a left their solar system to escape an escalating arms race that threatened to destroy their species and to find a place where they could live a technology-free life. They called themselves Ba'ku, which means "new beginning".