The Changeling attacks Odo
Ambassador Krajensky was replaced by a Changeling while he was en route to Risa in late 2371.
The Founder then traveled to Deep Space 9 and attended Benjamin Sisko's promotion to captain. He told Sisko a fake story of a coup on Tzenketh and that his first assignment as captain was to take him to the Tzenkethi to ascertain the situation.
En route, Krajensky was revealed as a Changeling and took control of the Defiant. The Changeling also impersonated Julian Bashir and Odo to avoid detection. The crew eventually regained control of the starship and Krajensky was killed by Odo, who in so doing became the first Changeling to ever harm another. "Krajensky"'s last words were "You're too late. We're everywhere..." (DS9: "The Adversary")
Odo's slaying of the Changeling provoked much debate and disagreement in the Great Link. In late 2372, they had Weyoun infect him with a disease to force him to return home and be judged. Odo was considered a traitor by the Jem'Hadar, as he had killed one of their gods. (DS9: "To the Death", "Broken Link")