The Fliis were a symbiotic species. In their native form, they were large, green, largely shapeless creatures with limited mobility. They invaded planets with multi-limbed inhabitants and bonded with them, allowing them greater mobility. They also connected to the host’s brain with a telepathic trance, making their removal impossible. The control signal operated on a Wi-Fi frequency and, by incorporating a visor into the fashion-wear, a visual link to the controlling body was created.
In the 20th century, the Fliis came to Earth and created Interconnected Clothing Experience, taking the form of leather jackets. The Eleventh Doctor thwarted the invasion by altering the pattern in the programming, setting himself as a new non-human template, causing the Fliis to detach themselves from the human bodies. (Fashion Victims)