Kes became a member of the Voyager crew following its subsequent ejection into the Delta Quadrant. She is from Okompa, a planet whose people were rumored to display unusual, supernatural abilities. She first displayed these cognitive flashes as the ship experienced turbulence due to a radiant shock-wave projected as the result of a nearby planet's demise. Her accompaniment on the away mission to investigate was crucial in detecting a chronological anomaly, which, once corrected realigned the crew to the moment before the shock-wave hit; Kes being the only one remembering the events as they occurred. With an insatiable desire to learn and grow, Kes undertook the creation of a hydroponic garden to compensate for dwindling food supplies and eventually became the medical assistant to the Doctor. The Doctor noted that Kes has an eidetic memory allowing her to absorb complex scientific and biological data at an incredible rate.
Kes developed a special relationship with the Doctor, raising the question whether or not he, as a hologram, had the rights and privileges afforded to the rest of the crew. She encouraged him to pursue hobbies and adopt a name for himself.
Jennifer Lien played Kes for 70 episodes on the Star Trek: Voyager television series.
From the time she boarded Voyager, Kes was partnered with the outspoken Telaxian, Neelix. They were an odd couple, but somehow it worked despite Neelix's jealousy. When on an away mission, Neelix became victim to a Vedian organ harvester who removed his lungs with a handheld surgical teleporter.
After going to great lengths to recover the stolen innards and save his life, Captain Janeway and the crew ran into a dead end with the lungs having already been grafted to another Vedian; however, with their advanced knowledge of biological systems and surgical prowess, the Vedians conducted a procedure using one of Kes's lungs as she was willing to do anything to prove her love to Neelix.
It became clear to Lieutenant Tuvok that Kes would need tutoring to hone her expanding mental abilities. What began as empathic senses and clairvoyant visions evolved into a full range of psionic talents expanding into telepathy and telekinesis at levels incomparable to Tuvok's own.
Eventually her body became unstable as it started to break down to a state of pure energy. With her new form wreaking havoc on Voyager, Kes used the dispersal of her mass to propel the ship out of harm's way and 700 light years closer to home.
In an unusual turn of events, Kes returned a few years later, appearing much older and very angry. She forced herself onto the ship and drained the warp core to transport herself back in time and change events in the past to send her past-self back to her homeworld. Tuvok began shifting between the past and present time streams and convinced Captain Janeway to investigate.
As Okompans grow at an accelerated rate, Kes had become elderly and the deterioration of memory caused her to become agitated and confused. Janeway had to remind her of the wonderful person she was and how appreciated she had been.