Yeerk


 * Yeerks are aliens.

Yeerks are small alien slug-like creatures with the ability to enter a creature through their ear canal, flatten themselves against the host's brain, and take complete control of their body. They can also read their hosts' memories effortlessly, allowing them to easily pass as the genuine article while the real organism's mind can only watch helplessly as their body is used to further the Yeerks' goal of conquering the universe under the aegis of the Yeerk Empire. They're quite fond of dabbling in genetic experimentation. No one on Earth (who doesn't have a slug in their brain) knows of their existence except for a small group of teenagers and an Andalite, collectively known as the Animorphs. Among the Yeerk leadership is Visser Three, who controls an Andalite. The Taxxons serve the Yeerks.