Vortex

DS9 Season 1 Episode 11
Air Date: April 18th, 1993

When a Miradorn is killed in one of Quark's holosuites, his murderer Croden from the gamma quadrant makes a claim that he has seen changelings before. Croden's home planet demands his return but Odo is intrigued with his possible origins and instead takes Croden to where he says the changelings are from. But he was really lying and brought Odo to where his daughter was kept in stasis to keep her safe from his home world. It turns out when someone commits a crime on his homeworld, he is put to death but his entire family is as well. His wife was already killed but he was able to save his daughter.

Odo finds a Vulcan science ship returning to the alpha quadrant and arranges for Croden and his daughter to go to Vulcan.

This was the first episode that really deals with Odo's origins beyond the possibly that he came from the gamma quadrant. They also have been using the term shapeshifter until this episode.

Quotes

"You think the whole galaxy is plotting around you, don't you? Paranoia must run in your species, Odo. Maybe that's why no one has ever seen another shapeshifter. They're all hiding!" - Quark