NEMESIS

The Replicators are introduced as the answer to a big question: Why don’t the Asgard swoop in and take care of the Goa’uld once and for all? Well, it turns out they have problems of their own. And now an Asgard mothership has been taken over by the bugs who are trying to land and infest Earth.

SMALL VICTORIES

The fourth season premiere resolves the story of the finale, as SG-1 learns that the Replicators have taken over a Russian submarine. Meanwhile Samantha Carter is recruited to travel to the Asgard homeworld and help them with some out-of-the-box thinking.

ENEMIES

Stopping the Replicators in our own galaxy may be one thing, but what happens when SG-1 is accidentally whisked away to another galaxy? Along with Jacob Carter, their ship encounters a Replicator-controlled vessel … which proceeds to infest their ship and set a course for the Milky Way. Again.

MENACE

After taking on the Replicator bugs more than once, SG-1 makes an astonishing discovery: an advanced android named “Reese,” who was left behind by her creator on a now abandoned world. It turns out Reese has a disturbing connection to the origin of the Replicators, who she regards as her “toys.”

UNNATURAL SELECTION

Studying Reese helped the Asgard figure out a way to summon all Replicators everywhere to “come forth” — right into an Asgard trap. The only problem? The Replicators turned the tables on the Asgard, and thanks to a little time-dilation technology have rapidly evolved from blocky insects to walking, talking humanoids, whose bodies are made up of many trillions of microscopic nanites.

NEW ORDER, PART 1

It was only a matter of time before the human-form Replicators found a way to strike back at the Asgard. But now led by the Replicator known as “Fifth,” their vendetta is also personal — and it’s aimed at SG-1 and Samantha Carter.

NEW ORDER, PART 2

Season Eight opens with a big 2-parter, as the team tries to save Jack O’Neill’s life — and Carter is captured by Fifth. Here we see more of the dreamscape that human-form Replicators are able to construct within a victim’s mind.

GEMINI

Fifth finally got his wish to be closer to “Samantha Carter” … or at least a version of her. The eighth season episode “Gemini” pairs Carter with her own Replicator twin (nicknamed “RepliCarter” by the fans). Together they work to develop a weapon that might eliminate the Replicator threat once and for all.

RECKONING, PART 1

The Replicator threat comes to a head in this epic 2-parter, as the enemy fleet finally arrives in force in the Milky Way Galaxy. The bugs demonstrate that it isn’t just the humans of Earth who have something to worry about, as they first take on the dominant power in our galaxy: the Goa’uld.

RECKONING, PART 2

In the exciting conclusion it’s Daniel Jackson who is a prisoner of the Replicators this time, as Stargate Command is flooded with techno-bugs. Meanwhile Sam and her father Jacob are forced to team up with an old enemy to unlock a powerful weapon left behind by the Ancients.

PROGENY

The Atlantis expedition had never encountered a Replicator, beyond a passing familiarity with SG-1’s past mission reports. Heck, they were in a completely different galaxy. So imagine the shock when Sheppard and his team learned that a potential new ally — the Asurans, a group living in a city very much like Atlantis itself — are in fact Replicators. The Pegasus Galaxy will never be the same.

THE REAL WORLD

After narrowly escaping from the Asurans the team discovers that they didn’t quite get away unharmed. One of their own has been infected by Replicator nanites, putting her into a dream world where she cannot tell reality from the Replicator-induced fiction.

THE RETURN, PART 1

After a ship of surviving Lanteans come home to Atlantis, Dr. Weir and the expedition she leads are forced to hand over the city and return to Earth. But the Lanteans’ hold of the city is short-lived when the Asurans show up on their doorstep.

THE RETURN, PART 2

Atlantis is now under Replicator control, with General Jack O’Neill and I.O.A. rep Richard Woolsey in enemy hands. The Atlantis team takes extreme action to return to Pegasus and reclaim their home.

FIRST STRIKE

Knowing that the enemy is determined to make another run on Atlantis, Earth command determines to send the Apollo to attack their homeworld of Asuras directly. The attack is devastating … but only enough to kick the hornet’s nest.

ADRIFT

The city-ship of Atlantis is floating through space after being forced to leave the planet Lantea. This episode is not Replicator-heavy, but it does play an important role in joining the third season finale with the next episode — which will be critical to the Replicator storyline.

LIFELINE

In desperate need of power to save the city and find it a new home world, Colonel Sheppard’s team embarks on an insane plan to sneak inside enemy territory and steal a Z.P.M.

THE SEER

The war with the Replicators is in full swing after Dr. McKay managed to reactivate their base command code. But when a seer visits Atlantis, the team receives a dire prophecy about the city’s fate.

THIS MORTAL COIL

Sheppard and his team come face to face with Replicator duplicates of themselves, and learn that the embers of a resistance movement inside of Asuran society are still burning.

BE ALL MY SINS REMEMBER’D

It all comes down to this. The battle lines have been drawn. On the one side: the Asuran fleet, arguably the most powerful force in the Pegasus Galaxy. On the other side: a motley alliance of humans, Wraith, and Travelers. The Battle of Asuras determines the fate of the Replicators — and the galaxy.

GHOST IN THE MACHINE

That underground cell of Asurans managed to survive the war, and eventually show up in Atlantis seeking help. For years these Replicators have been seeking out the mysteries of ascension, which they hope is possible for inorganic beings. And their leader is someone near and dear to Atlantis and Sheppard’s team.

STARGATE: THE ARK OF TRUTH

Just when you thought the Replicators were defeated and gone for good … some numskull has to think of a way to resurrect one of the galaxy’s greatest threats. The Replicators make a return — like we’ve never seen them before — in the first SG-1 movie, which is set after Season Ten.

The Ark of Truth also wraps up a 2-year storyline (unrelated to the Replicators), so if you plan to watch that arc you’re best to save this one for last.