The Makers were parasites at war with the Oon.
The Makers possessed people and restructured their bodies to make them more efficient. They could change the appearances of their hosts at will by redistributing mass and rearranging chromatophores in their skin. Whilst converting a host's body, the Makers could make the host forget the presence of the Maker. After conversion, the Maker destroyed the personality of its host body. The true form of a Maker was Y-shaped until it attached itself to a host. (PROSE: Halflife)