Possession was a term to describe someone or something having control over the body of another. While this normally had a negative connotation, not all possessions were the result of a malicious intent.
In 2371 Tuvok and Commander Chakotay were sent to explore a dark matter nebula. When they returned Chakotay was brain dead, but Chakotay's consciousness was actually floating around the ship. Commander Chakotay first possessed B'Elanna Torres in order to eject the warp core. He then possessed Captain Janeway in order to stop Tuvok and finally possessed Neelix to make a map. (VOY: "Cathexis")
The Komar were non-corporeal beings that lived in a dark matter nebula, located in the Delta Quadrant. Chakotay and Tuvok encountered the Komar and Tuvok was possessed. The possessed Tuvok also tried to trick Captain Janeway into taking Voyager into the nebula in 2371. (VOY: "Cathexis")
Neural parasites Edit
The Prophets and the Pah-wraithEdit
Selected DNA exchangeEditVOY: "Warhead")
Some Trill completely take over the host body, a full possession unlike the "blending" seen in other Trill. (TNG: "The Host") The rite of zhian'tara overseen by a Guardian allows for the past lives of the symbiont to possess a volunteer host for a short time. (DS9: "Facets") The Rite of Emergence allows a host to bring forth the personality and memories of a previous host, so the two personalities can interact. (DS9: "Field of Fire")