“Cold Lazarus” is episode seven of season one of Stargate SG-1.
SG-1 comes out of the stargate onto a planet where there are many clusters of blue crystals, most of which have been destroyed.
Colonel O’Neill discovers an intact cluster and touches it – touching it gives him a shock, knocking him unconscious, and a doppelgänger is created.
The double returns to Stargate Command and O’Neill is left on the planet.
The doppelgänger has some of O’Neill’s memories and visits O’Neill’s former wife, and when the real O’Neill returns to the SGC, things get confusing.
When they figure out what’s going on they must find the duplicate O’Neill before it starts emitting dangerous levels of radiation.
Not the scariest doppelgänger episode ever, certainly not an Evil Twin one.