Commander Tucker and Ensign Sato under Organian control
The Organians were a race of powerful non-corporeal beings that live on the planet Organia. Organians were once corporeal, but they eventually evolved a non-corporeal form. They implied that their desire to avoid physical pain was a reason for that.
For ten thousand years, they observed a planet that contained a silicon-based virus, and the reactions of species that encountered it, in an attempt to find a species with a higher level of intelligence. Among the species which the Organians observed as they attempted to deal with this deadly virus were the Klingons, Cardassians, and Humans.
In 2154, Enterprise NX-01 investigated a Klingon waste site on the planet, and a landing party consisting of Commander Charles Tucker III and Ensign Hoshi Sato contracted the virus. Following their protocol of non-interference, two Organian observers watched the crew's reaction to the situation by inhabiting the bodies of crew members, and subsequently altering their memories so that they had no recollection of the Organians' actions. One of the two observers, apparently the more senior of the two, felt that the Organians' protocols should be followed strictly; the other, who was impressed by the Humans' compassion, felt that the time had come for the protocols to be altered. The junior observer argued that intelligence alone was not a sufficient measure of a species' worthiness to be contacted. The senior observer routinely occupied the body of Lieutenant Malcolm Reed, while his associate occupied the body of Ensign Travis Mayweather, though all of the senior staff of Enterprise were possessed by the observers at one point or another.