The Velonans were a race of human from the Milky Way galaxy who, by the time of their discovery by the Tau'ri, were long dead. 400 years before their discovery, the Velonans were unable to defend themselves from the Goa'uld. The ascended Ancient known as Orlin provided them with an Orbital weapon to protect them from the Goa'uld.
After the threat was neutralized, the Velonans began to develop ways to use the weapon to conquer other worlds. After these violent acts, the Velonans were completely wiped out by the other ascended as a lesson to Orlin. (SG1: "Ascension")