Odo

2365: Became an investigator on the Cardassian space station Terok Nor
2369: Remained on the Station, when the Federation took over, as Chief of Security

One of a Hundred Changelings sent out into the galaxy by the Founders
Found adrift in the Denorios belt, brought to Bajor to be studied by Doctor Mora Pol
2371: Discovered the Great Link, later became the first Changeling to kill another
2372: Infected with a virus by the Dominion, judged by the Link, turned into a "solid"
2373: Turned back into a Changeling by the dying act of an infant Changeling
2375: Discovered that he was patient zero of the morphogenic virus, cured by Bashir;
Convinced the Female Changeling to end the war, rejoined his people & cured them