Mutable

Mutables, a.k.a. Shape-changers, Silhouette Shifters, Metamorphs, and myriads of similar names, are a mysterious species regarded as just a myth. Stories about them can be found on several worlds throughout the Humanx Commonwealth and the AAnn Empire territories, among others. They can assume the form of other species and live among them without raising suspicion.

Mutables describe themselves as caretakers in service of the Xunca: an advanced civilization which lived over a billion years ago and has long since left the galaxy. On each world in which the Xunca have been present, they have left a single Mutable to act as caretaker to the Xunca's mysterious machinery, the purpose of which is unknown even to the caretakers themselves.

Biology
In their natural form, Mutables resemble towering amorphous masses of silver fluid which can create eyes, tentacles and pseudopods as needed. They can assume the form of other species and live for hundreds of millions of years.

Mutables themselves don't know whether they evolved naturally or were created artificially by the Xunca. Their biological structure has been described as being closer to inorganic than organic.

Culture and society
Although they are not aware of their purpose, Mutables willingly act as caretakers to the Xunca's machinery, obeying the instructions of their long-departed masters. For hundreds of millions of years, many Mutables have observed the development of native species on the planets they have been tasked with guarding. Part of their duties include seeing that the Xunca's machinery remains hidden and undiscovered.

Like most sapients, individual Mutables differ from each other in terms of personality and interests. At least some are known to be friendly and willing to trust others. They have also been known to find their way into spaceships and visit each other's planets to converse and occasionally assist each other with their caretaking duties.

Appearances

 * Voyage to the City of the Dead, by Alan Dean Foster (1984)