Dagan, formerly known as Sudaria, was a planet in the Pegasus galaxy. When the Lanteans fled Atlantis after they lost the war with the Wraith, one of them left a Zero Point Module with the Quindosim, members of an order which belonged to the Sudarian society that worshiped the Ancients. Unfortunately, ten thousand years of cullings left the Sudarian society extinct, while the modern Daganians were at a renaissance level of technology. However, there was a portion of the population who still followed the ways of the Quindosim and worshipped the Ancestors.
After Dr. Elizabeth Weir from an alternate timeline was awoken from her stasis pod and supplied a list of planets with ZPMs to the Atlantis expedition, Major John Sheppard's team traveled to Dagan and eventually located the ZPM, however the new members of the Quindosim took it from them, hoping that the actual Ancients would one day return for it and that with their returns, the Quindosim would be greatly rewarded although the Quindosim were not aware of the fact that the Ancients had long since departed from the Pegasus Galaxy and would never return. (SGA: "The Brotherhood")