Ava Dixon was a Tau'ri-built Human-form Replicator, one of two models that Dr. Richard Poole made, as part of Project Archetype. She had no self-replication as a function and she was also immune to the effects of the Anti-Replicator gun technology. She was programmed for social interaction. Ava knew she was a replicator.
Replicator Ava was a copy of the real Ava Dixon, who died in a car accident in 2007; Poole programmed her with Ava's memories. In 2008, she worked with Richard Poole to produce a Replicator, but one day she received orders to destroy all evidence of their research by Henry Wallace, who had been arrested.
A few months before she made contact with Lt. Colonel John Sheppard and Ronon Dex, Ava had been checking on them when Wallace abducted Jean Miller and Dr. Rodney McKay. When the other Replicator managed to escape from them, Poole tried to turn him. Ava worked unsuccessfully with Poole to try to track down the rogue Replicator, and contacted Sheppard and Ronon on Earth to tell them everything about Project Archetype and the runaway Replicator. She worked with Sheppard to track down Poole's Replicator with Dr. Bill Lee. They found him, but were unable to capture him, as he Replicator Poole had masked his energy signature.
After Lee managed to crack Poole's computer code, he found information about Ava: that she had died a few months earlier, and the Ava they knew was a replicator. After they found the rogue Replicator, Lee and Shepard intervened so that Ava could stop him; she gave Sheppard a chance to attach a tracking transmitter on Replicator before beaming him into orbit. Ava knew she could not be released because (as a Replicator) she was a security risk. Lee transferred her entire consciousness to a virtual reality pod at Stargate Command where she could explore her world of illusion as she wished. Subsequently, her nanite body was scrapped and recycled. (SGA: "Outcast")