Rull

The Rulls are a combative extragalactic sapient species which has been in war against Humans for over a thousand years. Their appearance is similar to a white worm and they seem to be able to fly without wings. They're also capable of shapeshifting.

Appearances

 * "Cooperate, or Else!", by A. E. van Vogt (1942)
 * "The Second Solution", by A. E. van Vogt (1942)
 * "The Rull", by A. E. van Vogt (1948)
 * The War Against the Rull, by A. E. van Vogt (1959)
 * "The First Rull", by A. E. van Vogt (1978)