Worf was able to get the information about the Changeling splinter group from Odo, who sent a message from the Changeling home world, where the entire mass of the Great Link exist in one big ocean of goo. We know that the Changelings continue to exist in some form hundreds of years after the events of “Picard” because they’re referenced on “Star Trek: Discovery,” but that’s all we’ve really heard about them since the end of “Deep Space Nine,” when Odo returned to the Link in order to help cure a disease that was destroying his fellow Changelings. Sadly, we didn’t get a chance to see Odo because Auberjonois passed away in 2019, but knowing that he’s still out there, taking care of the Great Link after all of these years, is reassuring. (The only thing that would be better is if he got to leave and reunite with his old love, Kira Nerys, played by Nana Visitor.)
Originally, the Changelings called themselves “The Founders,” and they genetically engineered and trained two entire species to serve them: the Vorta and the Jem’Hadar. The Founders used the Vorta to handle all of their mundane and executive tasks, like interstellar butlers, while the Jem’Hadar were their soldiers, born addicted to a chemical called ketracel white. The Changelings and the Federation discovered one another because of a wormhole next to the planet Bajor, connecting the Alpha Quadrant (where the Federation exists) and the Gamma Quadrant (run by the Founders and their organization, the Dominion). Unfortunately, the Dominion are really into domination, and they try to take over the entire Alpha Quadrant before eventually being defeated by the Federation and their assembled allies and frenemies, led by Captain Benjamin Sisko (Avery Brooks) and the Cardassian leader, Damar (Casey Biggs).