A hidden planet where Altan Soong and his team built a community of synthetic life, the site of a standoff with the Romulans in 2399.
Coppelius is a planet in the Ghulion system that became home to a community of synthetic people after synths were banned in the Federation. Altan Inheim Soong, the son of Noonien Soong, and his colleagues lived there with the androids they had made. Among them were Soji Asha's sisters and Sutra, a synth with a powerful will, and the planet was protected by a hidden defence system.
In 2399 Jean-Luc Picard and the crew of La Sirena reached Coppelius while bringing Soji home. Sutra, believing the synths faced annihilation by the Romulans, built a beacon to summon advanced synthetic beings to destroy organic life. A Romulan fleet led by Commodore Oh arrived to wipe out the synths, and Riker led a Starfleet fleet to defend them. Picard persuaded Soji to shut the beacon down, and his body failed. His consciousness was moved into a new synthetic body, a golem, built on Coppelius.
Coppelius is the climax of Picard's first season. It shows the struggle for synthetic rights and gives Picard a new lease of life, linking him with Data's legacy.