Crashed to Earth in our year of 1965. Hibernated. Emerged in '98. Took human host bodies. For some unknown reason, started playing abrasive, instrumental surf-punk.
Little is known about what caused these humans to be chosen for "duty" by alien beings. Hosts enter a fugue state with compulsive tendencies which could be refered to as "Parasite-Induced-Somnambulistic-Trance" (or P.I.S.T.) and can be likened to sleepwalking. They have a strict doctrine of not communicating verbally with humans under any circumstances, and should be considered very dangerous.
Why creatures from outer space would neglect all of the usual stereotypes of alien invasion behavior- i.e.- slaughtering the masses, enslaving humanity, breeding giant lobsters- only to play in a "punk rock" band is not understood.