Changelings

Changelings, also known as The Founders, are an alien race from the Star Trek universe. They are called Changelings because of their ability to shape-shift. Their natural state is a liquid "protoplasm." Changelings have the ability to melt together to share information and emotions in a very intimate manner. The Changeling homeworld is covered in a sea of Changelings known as the Great Link. Changelings can turn themselves into almost anything and can flow through any gap in their liquid state. They have even been known to turn into convincing imitations of particular human beings. However, if a part of a changeling is separated from the whole, it reverts to the liquid state. In addition, a Changeling must regenerate, returning to its liquid form once every several hours.

The Changelings are native to the Gamma Quadrant. They are the rulers of the Dominion. They seek power because they were once persecuted by non-shape-shifters, whom they call "Solids." After the discovery of the Bajoran wormhole and the subsequent war between the Dominion and the United Federation of Planets, the covert Federation group Section 31 created a disease that prevented the Changelings from shape-shifting. When the Dominion was defeated, the Changelings were cured.

The Changelings were introduced in the Star Trek spin-off Star Trek: Deep Space Nine. Constable Odo, one of the regular characters on that show, is a Changeling.