The Vorta were once small timid ape-like creatures that lived in hollowed out trees and living in fear of the many predators that would hunt them for food. One day a changeling happened upon a Vorta family while it was running from an angry mob who was trying to kill it. The Vorta family took the changeling in and hid it from the mob, saving its life and earning its gratitude. In response for their kindness towards a changeling, something the founders rarely, if ever, experience from solid life-forms, the changeling promised them a position of power within the Dominion (DS9 episode: Treachery, Faith, and the Great River).
The Vorta, thanks to the genetic modifications made by the founders, have excellent hearing, though they are tone deaf, they are also colour blind and have poor eyesight (DS9 episode: Favor the Bold).
They also have a limited sense of taste; they cannot taste anything beyond the nuts, fruits and berries of their home world. This is to remind them of where they came from and what they owe the founders (DS9 episode: Treachery, Faith, and the Great River).
Each Vorta is in charge of distributing a drug known as Ketracel-white among the Jem'Hadar under their command, the event is somewhat of a ritual with the Jem'Hadar pledging their loyalty to the founders before receiving their vials of the drug (DS9 episode: To the Death).
The Vorta care little for the Jem'Hadar under their command, seeing them as no more than tools to get a job done and will quite happily sacrifice them all in order to prolong their own survival (DS9 episode: Rocks and Shoals).
The Vorta are cloned by the founders, when one dies, they are replaced by their copy, offering them a kind of immortality. On occasion, a clone is "defective" and does not behave like a typical Vorta, the reason for this is unknown, but any defective Vorta are killed without question (DS9 episode: Treachery, Faith, and the Great River).
The Vorta are 'built' with a self termination device in their brain stem, this is in case a Vorta is captured, though they are ordered to use it if they turn out to be defective. They are made to believe that the process is painless, but that isn't the case (DS9 episode: Treachery, Faith, and the Great River).