The Roswell Incident was the name given by Human conspiracy theorists in the late 20th and early 21st centuries to an alleged alien encounter in Roswell, New Mexico in 1947. Though it was denied and dismissed by all official agencies the story continued to be told and spread.
According to the conspiracy theory
An alien spacecraft (an unidentified flying object) crash-landed in the desert near the small town of Roswell in 1947. The US armed forces arrived to investigate and took charge of the area, sealing it off and begining a clean-up operation. Everything was removed and one officer stated that the wreckage was a crashed weather balloon to cover-up the incident. The real wreckage of the craft, as well as a farmer who had discovered it, was moved to Hangar 18 inside of a top secret military base.
What actually happened
The Ferengi shuttle Quark's Treasure was accidentally propelled backwards through time while on a trip to Earth to deliver Nog to Starfleet Academy in 2372. Aboard the shuttle were Quark, Rom, Nog and, unbeknownst to the other three, Odo. The ship crash-landed in the desert near the small town of Roswell in 1947. The craft's systems were slightly damaged but it was still flyable. Witnesses did report that a flying saucer had crash-landed despite the shuttle not being in any way saucer-like. The US Army Air Corps quickly formulated a story about a misidentified weather balloon which was fed to the press to cover up the incident.
The craft and three unconscious Ferengi passengers were transported to Roswell Air Force Base. Odo disguised himself as a dog and infiltrated the base to rescue the Ferengi. The Ferengi awoke in perfect health, and once they had reset their universal translators, Quark began to try to sell futuristic technology to the primitive Humans in an attempt to a) turn a vast profit and b) make the Ferengi Alliance the ultimate force in the galaxy by changing history.
Then things began to take a turn for the worse and the Humans lost their patience with their new guests; they began using drugs and threats of violence and dissection on the Ferengi. Luckily the Ferengi were aided in their escape by Odo and sympathizers Nurse Garland and her boyfriend Jeff Carlson.