Kes was an Ocampan, an elf-like race native to the Delta Quadrant, with a lifespan only 1/10 that of humans. She was taken into the Starship Voyager crew with her partner, Neelix. Kes has mysterious metaphysical powers that were relatively unknown, even to herself.
Kes developed a close relationship with The Doctor during her time as an assistant medical technician.
She left the Voyager crew when she "evolved" into a different state, but before she left she threw Voyager 20 years closer to Earth. (The Gift). She visited Voyager one more occasion, in a time-travel story.