Tracer

A tracer is a highly trained Ramuran agent assigned to track down and retrieve those who attempt to leave their homeworld (located in the Delta Quadrant).
They are trained to be experts in weaponry, surveillance, and fighting skills.

They hide themselves and their ships with polarization cloaks, and they use computer viruses to eliminate any records of their presence. They are armed with neurolytic emitters, devices that erase the memories of their targets, making them more cooperative.
Tracers are extremely persistent- the disgrace of returning home empty-handed would be too great to bear.

In 2374, one tracer tracked a fugitive to the USS Voyager. After fulfilling her mission, the tracer found that she had developed feelings for Commander Chakotay, and returned to Voyager as a fugitive herself.

She was hunted by more tracers, one of whom infiltrated Voyager and erased her memories. As a result, all aliens went back home to Ramura.