The Entity was an electrically-based life-form from P9C-372. It had returned to Earth through an outgoing wormhole as wave energy riding on MALP telemetry. It accessed the SGC's main computers, sustaining itself through secondary power systems, growing exponentially, and overloading the base mainframe. It created a "nest" in the MALP room, expanding within the computer systems, and eventually it entered Carter as a host, bringing the base to quarantine at DEFCON level 2.
Through Carter, the Entity was able to communicate by typing messages into a voice-enabled laptop computer, and it insisted that once it had entered Carter's body, it was impossible for it to leave. The Entity responded to questions about its identity with, "I am within," and revealed that the radio energy emitted by the MALP had been a contagion to its planet. It had come through the gate intending to preserve its own world by destroying Earth. In fear of O'Neill's threat of retaliation, however, it chose to spare its world by allowing itself to be killed. O'Neill fired the two shots of the zat gun that destroyed the Entity within Carter, and although Carter's body could be sustained, she was believed to be gone until it was discovered that the Entity had transferred her consciousness back into the nest before it had been destroyed. Dr. Fraiser was able to restore Carter's consciousness to her body from the electronic nest.
Portrayed by: Amanda Tapping
Cross Reference: DEFCON, P9C-372
Episode Reference: Entity