The Asgard were an extremely advanced race, one of the members of the Ancient Alliance of four great races. They resembled Roswell Greys and were a species who had regularly monitored and studied human development, having visited Earth without detection by Earth's satellites or telescopes. They were a friend to all, protector of all, except the Goa'uld, with whom they had been at war and with whom they had enforced an uneasy peace.

As a species, the Asgard were a dying race. They reproduced exclusively through a process of enhanced cellular mitosis (cloning), and for nearly a thousand years had been physically incapable of achieving cell division through meiosis (sexual reproduction), a fact which accounted for their similarity in appearance. Asgard DNA was programmed to grow a clone to maturity in just three months, but the clone body was essentially an empty shell. As each Asgard's body failed, his consciousness was transferred into a newer, younger cloned version of himself. Human bodies are similar to the Asgard's original form thousands of years ago, however the lack of genetic diversity through thousands of years of cloning had caused a gradual deterioration which led eventually to the fall of the Asgard civilization when the problem of diminishing returns in cloning technology could not be resolved. Heimdall, an Asgard scientist, had been researching Asgard physiology and genetic manipulation through controlled mutation in order to stave off genetic degradation and preserve the Asgard race. Loki, another Asgard scientist and geneticist, had taken human abductees from Earth, hoping to use the human physical makeup as a template to construct a superior clone, until his unsanctioned and unsuccessful experiments were terminated by Thor.

The Asgard had inhabited many planets across their own galaxy and ours, including Hala, Orilla, and Othala in the galaxy of Ida. O'Neill first encountered the Asgard on Othala after acquiring the knowledge of the Ancients from the Ancient repository on P3R-272, and the Asgard, who had also studied Ancient technology, were able to remove the knowledge and restore his mind as before.

Advanced Asgard technology includes legendary motherships, transportation beams, sophisticated cloaking and invisibility devices, holographic projection, stasis pods, anti-gravity devices, powerful weapons, time dilation technology, the ability to control the stargate without a DHD and to override Earth's iris, as well as the ability to restore life shortly after death. Much of their technology is based on smooth rounded stones which can control ship functions as well as holographic projections, recordings and communications, and the stargate itself.

A benevolent race, the Asgard had protected more primitive cultures through devices such as Thor's Hammer, or through membership under the Protected Planets Treaty. On protected worlds such as Cimmeria and K'tau, the Asgard used holographic images which took on the role of Norse gods such as Thor and Freyr to guide the planet's development. In reality, Thor was the Supreme Commander of the Asgard fleet and a member of the Asgard High Council. He became a friend and ally of Earth, establishing diplomatic ties and negotiating with the System Lords for Earth's inclusion in the Protected Planets Treaty. Although the treaty forbade Asgard interference on behalf of protected worlds, it remained in force until the rise of Anubis because the Goa'uld System Lords feared the power of the Asgard.

The Asgard, however, had faced a far more dangerous enemy in the Replicators, a plague that stretched across their home galaxy and left limited resources to enforce the treaties with the Goa'uld. Asgard overconfidence in their own technology had been their undoing, and several times they turned to Earth for help in defeating their enemy. When Thor's mothership, the Biliskner, became infested with Replicators, SG-1 fought to destroy the threat to Earth by crashing the ship into the Pacific. Thor again sought help from Earth when Replicators threatened his homeworld, and Carter's less sophisticated approach provided a deception to save Thor's planet, granting a small victory in the Asgard's ongoing battle. Using information gathered from the examination of the android Reese, the Asgard devised a plan to summon the Replicators to the original Asgard homeworld of Hala to trap them within a time dilation bubble. However, the plan failed and once again Thor turned to SG-1 for low technology assistance in resetting the time dilation device. When the Asgard had evacuated Hala and relocated their population, they had carried numerous stored minds aboard the computers of Asgard ships and fled to the new homeworld of Orilla. There the minds were placed in cloned bodies and the new colony of Orilla became the last chance of rebuilding the Asgard empire. The Asgard had hoped to eliminate the Replicator threat by collapsing Hala's sun into a black hole that would swallow the planet, but this plan also failed and the Replicators escaped to threaten Orilla. Once again Thor relied on SG-1, and the Ancient knowledge within O'Neill's mind made possible the development of a disruptor weapon which eliminated the threat to Orilla and preserved the Asgard race.

SG-1 had also helped to rescue Thor when he was captured by Osiris and Anubis and his consciousness was downloaded into Anubis's mothership. In gratitude, Thor offered support for the SGC against maneuvering from rogue elements of the NID, and he shared Asgard-designed technology including shields, weapons, transport beam technology, and a hyperdrive for use on the Prometheus. When Fifth and the Replicators threatened to destroy the Alpha Site, Thor also offered a modified disruptor satellite, designed to prevent a large scale Replicator attack by ship, which eliminated Fifth and spared the base, and he returned to assist Carter in modifying the disruptor weapon to override the cipher that gave the Replicators immunity to its technology.

Following the destruction of the Replicators, the Asgard continued to maintain contact with Earth, however communications became less frequent as urgent affairs drew the attention of the Asgard elsewhere. When familiar allies such as Thor and Heimdall were attending to sensitive matters in a neighboring galaxy, Kvasir cooperated with the SGC in their place. Kvasir offered the loan of an Asgard energy weapon to seal a rupture in the space-time continuum that was causing a ripple effect between alternate realities, and as Kvasir cooperated with Carter aboard the Odyssey in an attempt to disable the supergate and prevent an Ori invasion, his Asgard vessel joined the allied armada in the battle against the Ori warships.

Despite the heroic efforts of their best scientists, however, the Asgard race was facing extinction. Having made too many irreversible mistakes in their development, their final attempt to solve the physiological degeneration of the Asgard race had left each of them with a rapidly progressing disease. Ascension was not an option, since they had made the choice generations ago to extend their lives through science, taking any natural physiological evolution necessary for ascension out of the equation. As a race, they planned to end their lives in a kind of mass suicide before their degeneration and suffering had gone too far. Although not all on the Asgard High Council agreed, many Asgard considered the humans of Earth to be the Fifth Race in whom the hope for preserving the future lay. SG-1 was invited to Orilla where Thor and the Asgard installed all their knowledge and all their most current technology aboard the Odyssey in what would be their final legacy. As the installation of the upgrades was completed, however, three Ori warships appeared above Orilla, and to ensure that their knowledge and technology did not fall into the wrong hands, the Asgard made the deliberate decision to end their civilization. In a massive planetary explosion, Orilla disintegrated, and the Asgard race was gone.

Cross Reference: Adara System, Aegir, Ancient Alliance, Anti-Gravity, Asgard Energy Weapon, Asgard High Council, Asgard Mothership, Asgard Stones, Asgard Transport Beam, Biliskner, Black Hole, Cimmeria, Cimmerians, Clones, Disruptor, Energy Generator, Fifth Race, Freyr, Hala, Hall of Mjollnir, Hall of Thor's Might, Hall of Wisdom, Heimdall, Holographic Projection, Hyperspace, Ida, Invisibility, The Daniel Jackson, K'tau, Kvasir, Loki, Odyssey, The O'Neill, Young Jack O'Neill, Orilla, Othala, PX3-595, Pamela, Penegal, Prometheus, Protected Planets Treaty, Reese, Replicators, Runes, Stasis, System Lords, Thor, Thor's Hammer, Time Dilation Device, Werner, Zyang Wu

Episode Reference: Thor's Hammer, Thor's Chariot, The Fifth Race, Fair Game, Point of View, Shades of Grey, Nemesis, Small Victories, Red Sky, Fail Safe, Revelations, Descent, Prometheus, Unnatural Selection, Disclosure, Fragile Balance, New Order, Covenant, Gemini, Reckoning, Ripple Effect, Camelot, Flesh and Blood, Unending