Gelflings are a race of elf-like creatures native to the planet of Thra. The term Gelfling derives from the term "Ghel-lflainngk" roughly translates to "those who live without knowledge of the future," according to The World of the Dark Crystal documentary. They love music, dancing and creating joy in their lives.
Ages ago, Gelflings could fly. However, the female Gelflings have developed wings that allow them to glide and flutter. Males do not have wings and free flight is not possible. The female's wings retract and can be concealed under the clothing.
The Gelflings once formed a happy and prosperous civilization on Thra. Their society was strong. However when the Crystal cracked and the Skeksis came into power, the Gelflings soon found themselves under Garthim attacks as they were captured and taken to the Castle of the Crystal. In the castle their living essence would be drained. The Skeskis found when consumed, the Gelfling essence had an age-reversing effect. The Gelfling captives, drained of the essence, would then become slaves to the Skeskis. Skeksis do not think highly of Gelflings at all and find them repulsive and hideous.
For once the Gelflings thought of the future and feared that if the Crystal remained unhealed, the Skeksis' rule would continue. By ways of magic and ritual the Gelflings created The Prophecy of the Crystal on the Wall of Destiny in the Gelfling city. The prophecy committed them to heal the Crystal at all cost.
When the Skeksis heard of the threat, they eliminated the Gelflings, sending the Garthim to hunt down the Gelflings in a mass extermination. Only two young Gelflings, Jen and Kira, survived thanks to their parents hiding them. It was these two, years later, who traveled to the Castle of the Crystal and put an end to the Skeksis' savage rule by fulfilling the prophecy. Jen and Kira then became the rulers of Thra and began to restore the Gelfling race.
The only Gelfling characters seen in The Dark Crystal are Jen, Kira, and Kira's mother (in a flashback). Power of the Dark Crystal was to have featured the return of Kira and Jen as rulers of Thra along with a Gelfling outcast and others. Larh and Neffi are two Gelflings featured in the Legends of the Dark Crystal graphic novel series. The Dark Crystal: Age of Resistance features Gelflings in a time before they were wiped out by the Skeksis.