Changeling

The Changelings are liquid-based, shapeshifting lifeforms native to the Gamma Quadrant of the Milky Way Galaxy. Their homeworld was, apparently, a rogue planet within the Omarion Nebula (which has since been rendered uninhabitable by the Obsidian Order and the Tal Shiar in the Battle of the Omarion Nebula).

A Changeling's natural state is its liquid form, which it must revert to every 16 hours in order to regenerate. Changelings can, however, take virtually any form (typically limited by their mass), ranging from humanoid aliens to fog to reflective surfaces.

The Founders of the Dominion are Changelings, and make up the majority of the Dominion. Changelings prefer to think of themselves as a drop (the individual) in the larger ocean (what they call the Great Link). A Changeling, therefore, typically has no sense of individual identity. Being a liquid-based lifeform, in order to link with other Changelings they simply revert to this state and the liquid blends together, creating a link between them.

At one time the Founders were peaceful and explored the galaxy. But they were persecuted by some of the solids, and they came to believe that the only way to protect themselves was to conquer those around them. Solids (mono-form humanoids) called the Founders "Changelings" as an insult, but the Founders took the name for themselves as an act of defiance.

Long ago, the Founders sent out 100 infant Changelings in order to gather information and explore, to return later and share what they have learned. The Founders did not expect any to return until the late-27th century. Odo and Laas were among the 100.