Changelings in their natural state appear as a golden coloured liquid. Some Changelings can only maintain other forms for a limited amount of time. Odo for example had to return to his natural state every sixteen hours to regenerate, while the Female Changeling could maintain the same form for weeks.
The Changelings possessed a remarkable shapeshifting ability, able to perfectly mimic other lifeforms and objects such that even advanced sensor technology such as that of the Federation during the latter-half of the 24th century was unable to detect Changelings when they were mimicking other forms. They could also mimic reflective surfaces, clouds, fog and even fire.
It was possible to interfere with their abilities to shapeshift. While they were highly resistant to phaser and disruptor fire, specifically tuned phaser sweeps could discomfort a Changeling enough to force it to revert to its nature state. The Obsidian Order also designed a device that would prevent a Changeling from changing and it was believed by Starfleet that exposure to polaron radiation would force a Changeling to its natural state.
When small parts of a Changeling was separated from the whole it did not have the ability to maintain its form and reverted to its natural state. For that reason blood screening was used by several governments, such as the Federation and Klingon Empire under this theory as any blood removed from a Changeling would soon revert to its nature state.
- Interestingly bloodscreening have never been shown to have any success and the only times it 'detected' a Changeling the results were faked.
In their natural state Changelings are able to "link" to each other, merging so to share thoughts and feelings. Even in this some individuality was retained and individual Changelings could prevent the complete sharing of their knowledge and information or even mislead other Changelings.
At some point in their past the Changelings were restricted to one form, which they refer to as being a "solid". After they became shapeshifters they began to be prosecuted by other species. They were referred to as "Changelings", which was meant to be a form of insult but instead they took it as their new name in an act of defiance. This history inspired their founding of the Dominion, of which they would become known as the Founders and their goal to bring order to the galaxy. Due to their past the Founders had a great mistrust of solids.
At some point the Founders sent out one hundred infant Changelings to explore and gather information and return to share what they learnt with the Great Link. The Founders did not expect to see any results of this mission until the late-27th century.
During the 24th century, the Founders' homeworld was on a rogue planet in the Omarion nebula before they abandoned it after the Obsidian Order and Tal Shiar planned to attack and wipe out the Great Link. They moved to a new planet at an unknown location. It is unknown whether or not the planet in the Omarion nebula was the Founders' original homeworld or simply a location the Great Link went to so to isolate itself from the rest of the galaxy.
After contact with the Alpha Quadrant a morphogenic virus was created by Section 31. Infecting Odo the virus was spread through the link allowing to spread to most of Changelings. Unable to devise a cure the Founders were face with extinction until Odo and the Female Changeling came to an agreement that saw her surrender her forces ending the Dominion War and standing trial for her crimes in exchange for Odo returning to the Great Link and curing the other Founders.
- DS9: "The Forshaken"
- DS9: "What You Leave Behind"
- DS9: "The Adversary"
- DS9: "The Way of the Warrior"
- DS9: "Chimera"
- DS9: "Homefront"
- DS9: "The Die is Cast"
- DS9: "Apocalypse Rising"
- DS9: "Paradise Lost"
- DS9: "Broken Link"
- DS9: "The Search, Part II"
- DS9: "The Search, Part I"
- DS9: "Treachery, Faith and the Great River"
- DS9: "Extreme Measures"