According to Norse mythology, Loki is the god of mischief. Among the Asgard, Loki is a scientist, a former geneticist with the Asgard Ruling Council who was stripped of his stature and banished after being caught performing unsanctioned experiments on humans.
Loki believed that his methods were necessary to advance vital Asgard cloning technology that would preserve the Asgard race. Over a period of several years, Loki had abducted humans from Earth, hoping to use the human physical makeup as a template to construct a superior clone. Abductees recalled a feeling of paralysis and weightlessness, being scanned by four glowing green globes that floated around them, and seeing aliens with small grey bodies and large dark eyes. Abductions usually lasted for a period of seven days, and Loki created a clone to replace each abductee during that time so as not to arouse suspicion before the individual was returned. Clones faced genetic breakdown due to Loki's inept methods, and were not expected to survive beyond the week.
Loki's experiments ceased 19 years ago, but he returned without the knowledge of the Asgard High Council and abducted O'Neill, hoping that his advanced DNA held the key to solving the problem of genetic deterioration. He created a clone of O'Neill, however a marker in O'Neill's DNA prevented the clone from maturing properly, and Young Jack O'Neill aged to only 15 years. When Loki attempted to return O'Neill to his home, SG-1 confronted him and summoned Thor. At O'Neill's request, Thor was able to repair Young O'Neill's DNA to allow him to survive, and Thor detained Loki, promising that he would be punished.
Voice of Loki: Peter DeLuise*
*Cameo by Peter DeLuise: Director, Writer, Producer
Cross Reference: Asgard, Clones, Young Jack O'Neill, Pamela, Thor, Werner, Zyang Wu
Episode Reference: Fragile Balance