In Star Trek: Insurrection, the immortal alien people protected by Picard are the Ba’ku.
The Ba’ku live on a remote planet whose rings emit metaphasic radiation. Exposure to that radiation continually restores their bodies, giving the settled population an effectively immortal lifespan. Starfleet officers discover that the Son’a and Federation officials plan to relocate the Ba’ku so the radiation can be harvested for medical benefits elsewhere.
Captain Jean-Luc Picard rejects the forced relocation and defends the Ba’ku’s right to remain on their homeworld. The conflict raises ethical questions about whether a larger population’s potential medical gains can justify violating the rights of a small, peaceful community.
The Son’a are not the protected people; they are the antagonistic group seeking the radiation. Remans appear in Star Trek: Nemesis, and the Ocampa are associated with Star Trek: Voyager. The Ba’ku were created specifically for this 1998 film.