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During an off-world mission Colonel Sheppard unknowingly becomes host to an alien entity, which infects others in Atlantis and afflicts them with terrifying nightmares.

FAN RATING - 8.33 
NIELSEN - 0.9 
DVD DISC: Season 4, Disc 1
WRITTEN BY: Robert C. Cooper
DIRECTED BY: Robert C. Cooper
GUEST STARS: Jewel Staite (Jennifer Keller), Claire Rankin (Kate Heightmeyer), David Nykl (Radek Zelenka), Kavan Smith (Lorne), Linda Ko (Med-tech), Yee Jee Tso (Technician)
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  • "Doppelganger" was nicknamed "Nightmare On Atlantis Street" around the show's production office.
  • "Well, we're finally in prep. Rob is up first – writing, directing, and producing 'Doppelganger.' I also hear he'll be working the catering truck every second day while the episode is in production. 'Doppelganger' shoots first but will air sometime after the opening Adrift-Lifeline-Reunion triumvirate. Once he's done, he'll be moving over to SG-1 and start prepping Ark of Truth which, incidentally, he'll again be writing/directing/producing. Show-off." (Executive producer Joseph Mallozzi, in a post at his blog)
  • "I've always been fascinated by nightmares and dreams. So that's what this is about. It's about an alien entity that lives in crystal form. I've kind of paid a little homage to 'Cold Lazarus' and said, 'Well, OK – there's something that we've established in the Stargate universe that we've never really dealt with before. And that is, again, lifeforms can exist in that state.'"

    "O'Neill went out, touched a crystal and all this stuff happened. We've never done that again. And I thought, 'Well, wouldn't it be interesting if we found another crystalline life-form like that.' But in that case we were kind of lucky that it had reasonably good intentions. There was a sinister aspect to it in that we didn't know what was going on, but at the end of the day it was kind of just curious. So I took the flip side of that and said, 'What if it's a psychopath? What if it's truly evil?' And it induces some pretty freaky nightmares."

    "... What would our characters dream about? The fun part of the episode is, because it's Sheppard that initially engages and touches the crystal, and thus unleashes the entity on everyone, the physical form it takes in the nightmares is Sheppard. And so everyone is having these nightmares that are being pulled out of them by the entity, but Sheppard is appearing in those dreams as the sort of negative inciting force."

    Cooper reached back not only to the first season of Stargate SG-1 in conceiving the story, but to his own childhood as well. "My dad took me to see Jaws when I was seven years old. I was seven. There's a line in the script: one of McKay's histories is that his dad read him 'Moby Dick' when he was seven years old. The line was: 'What was the man thinking?!'"

    "I think I probably didn't sleep for two years. Honestly, I probably needed therapy! This was not the sort of thing you did back then, but I probably should have gotten some sort of counseling. But instead I spent my nights thinking to myself, 'One day I shall control the power that left me so terrified!'" (Executive producer Robert C. Cooper, in an interview with GateWorld)