Star Trek: 10 Things You Didn't Know About Odo
6. Unknowns Of Unknown Sample
Through morphology, we get the etymology of 'Odo'. Studied for his shape, for his shapeshifting, by Bajoran scientist Doctor Mora Pol during the Occupation, it was a loose translation that gave the changeling his name. "Unknown sample" on the lab flask in Bajoran became "Odo'ital," meaning "nothing," in Cardassian. Odo'ital was then divided like a Bajoran name — Odo Ital — before being abbreviated to Odo.
Like his name, Odo knew nothing about his origins at first (and neither did the writers). The June version of the Deep Space Nine Series Bible states that,
Although he doesn't know anything about his species, he is certain that Justice [sic] is an integral part of their being… because the necessity for it runs through every fiber of his body, a racial memory.
Odo would reiterate that point to Sisko in Necessary Evil, adding, and not without irony in hindsight, "It's the only clue I have to what kind of people they are".
The June Bible also notes that,
Fifty years ago, with no memory of his past, [Odo] was found alone in a mysterious space craft that appeared near the Denorios asteroid belt.
A line that never made it to air from the revised final draft script of Emissary of 10 August 1992 equally makes mention of "a vessel of unknown origin," which appeared in the Denorios belt "thirty-two years ago". It was "carrying a single lifeform, a species never encountered before". That's not an explicit reference to Odo, but it's close enough.
In any case, the Denorios belt bit stuck, but the ship part didn't. As Sisko noted in The Begotten, the Founders apparently just launched their one hundred "helpless creatures out into space" as is. What happened to the other 97 of them? Nobody knows.