Stargate: Every Villain Ranked Worst To Best

The Genii were one of the first enemies that the Atlantis team provoked in the Pegasus Galaxy (except the over-arcing Wraith, of course). The Genii posed as uninteresting farmers to outside eyes for a while, but it was revealed that they had large cavernous cities beneath the surface of their planet, where they were at a WWII level of technology. Indeed, they were just putting the finishing touches on their first atomic weapons.

They had built these cities to be hidden from Wraith culling and were prepared to fight before the next great harvest of the galaxy. At first they tried to act as allies to the Atlantis Expedition, but the two groups lied to each other and fell foul of one another. In the first season of Atlantis, the excellent two-parter 'The Storm' and 'The Eye', they tried to take over Atlantis while it was trying to ride out a colossal storm, a bitter combat between the two of them saw the Genii Commander Kolya swear his revenge on Shepard.

The Genii would crop up a few more times but would phase out as a threat when Layton Radim took over their society. After that, they were mentioned a few more times but never really posed a threat again.