Loki, an Asgard geneticist, had been performing unsanctioned experiments designed to advance vital Asgard cloning technology that would preserve the Asgard race. His methods involved abducting humans and replacing them with clones for a period of several days while he studied the human genetic code. O'Neill's genetic coding had been safeguarded by the Asgard, who had placed a marker in his DNA to prevent any attempts at genetic manipulation. When Loki abducted and cloned O'Neill, the genetic marker prevented the clone from maturing properly, and the young clone aged to approximately 15 years.
Young Jack O'Neill believed himself to be the real O'Neill who had been inexplicably regressed in age, and except for a tiny abnormality, his DNA was virtually identical to the colonel's. However, further testing revealed that he was in fact a clone, and due to an unstable genetic structure that was a result of Loki's inept methods, he was slowly dying. Young O'Neill assisted SG-1 in apprehending Loki, and at O'Neill's request, Thor repaired the DNA of the young clone, enabling him to survive and to continue to mature at a normal human rate. The Air Force provided for him, and Young Jack O'Neill decided to enroll in Mountain Springs High School, to embrace the high school experience, and to take advantage of the opportunity to live his life again.
Portrayed by: Michael Welch
Cross Reference: Asgard, Harlan Beck, Clones, Loki, Jack O'Neill, Pamela, Werner, Zyang Wu
Episode Reference: Fragile Balance