Jonathan O'Neill

Incorporating all of Jack O'Neill's memories and personality, the O'Neill clone was conceived by the Asgard scientist Loki and transported to Earth. While Loki studied the real O'Neill, his clone was to take his place on Earth for one week's time. For O'Neill's own protection, the Asgard had placed a marker in his DNA to prevent any attempts in genetic manipulation. Loki, not realizing this, duplicated O'Neill nevertheless -- and as a result, the clone was rapidly matured only to about age 15, instead of the colonel's actual age. The duplicate, not realizing he was a clone, went to the S.G.C. looking for answers, and soon discovered a flaw in his DNA that was going to kill him. At O'Neill's request, Thor repaired the genetic defect. The United States Air Force took O'Neill's young clone under their wing to provide for his future, and he returned to high school to live his adolescence over again.