When the Replicators found Reese, they hailed her as their creator, and found that she possessed certain advantages over the standard insect-form Replicators. They used her nanite cell technology to create First, to serve as their leader. His abilities enabled him to deactivate the Asgard time dilation device.
When SG-1 entered the planet to repair the time dilation device after being asked by Thor, the first five Human-form Replicators greeted them. After some talk, the Replicators probed the mind of the team to learn more about them. Afterwards SG-1 was "invited" to dinner with the Human Forms, during which they got more information about their creation. When SG-1 worked together with Fifth to reactivate the Time dilation device, First revealed that they had made a fool of his "son". (SG1: "Unnatural Selection")