SG-1 is a multi-purpose task force whose functions include first contact, reconnaissance and combat, diplomacy, initial archaeological surveying and technological assessment. Its standing orders are as follows:
- Open and maintain diplomatic negotiations with other worlds
- Obtain technologies to help defend Earth against the Goa'uld and other aggressors
SG-1 has, both successfully and unsuccessfully, executed these orders for the years Stargate Command has been operating.
SG-1's original team consisted of Colonel Jack O'Neill as commanding officer, along with Carter, Jackson and Teal'c.
In the team's sixth year of operation, after Dr. Jackson had died of radiation poisoning and ascended, Jonas Quinn of Langara took his position. Competent, reliable, and able to absorb vast amounts of information in a considerably short period of time, he was an asset and a testament to his people.
One year later Daniel fell from the ascended plane, and Jonas was called back to his homeworld to lead the political negotiations of his country, Kelowna.
In SG-1's eighth year of operation Colonel O'Neill was promoted to the rank of Brigadier General. He took command of the S.G.C., leaving SG-1 as a three-person unit, though he did go off-world when a mission required his presence.
In the ninth year, Colonel O'Neill was promoted to General Hammond's position as overseer of Homeworld Security in Washington. By this time, Lieutenant Colonel Cameron Mitchell had recovered from his injuries after defending SG-1 from Anubis's forces in Antarctica one year before. Cameron, who had been offered any position in the S.G.C. by O'Neill, chose to join SG-1, but he was surprised when he learned he was to lead the unit, and it was going to be a fresh team.
SG-1 had disbanded. Teal'c had returned to Dakara to aid his people in the development of the new Jaffa government, Carter was assigned to Area 51's research and development labs, and Jackson had moved on as well. With the presence of a new threat,however, Mitchell was eventually successful in reassembling the unit.
In the tenth year of operation the team was expanded, with the addition of Vala Mal Doran as the fifth team member. A former host to the Goa'uld Qetesh, Vala was rescued by the Tok'ra, who removed the symbiote. Vala lived mostly on the wrong side of the law, going from planet to planet as a thief and a con artist before she met Daniel Jackson and, later, joined SG-1.
SG-1 is largely responsible for the destruction of several powerful Goa'uld, including Apophis and Anubis.
Children of the Gods - SG-1 is formed by General Hammond. Commanded by Colonel Jack O'Neill, their mission is to establish diplomatic relations with other worlds and procure technology that will aid in the fight against the Goa'uld.
The Fifth Race - When Jack O'Neill succumbs to the Ancients' repository of knowledge Colonel Castleman is given command of the team.
Shades of Grey - After stealing a piece of weapons-disabling technology from Tollana, O'Neill goes into early retirement, leaving the unit to be commanded by Colonel Makepeace.
Meridian - Daniel Jackson ascends to a higher plane of existence, leaving SG-1 a three-person unit.
Redemption, Part 1 - SG-1 attempts to integrate several officers into their unit but no one seems to fit the bill.
Redemption, Part 2 - Jonas Quinn joins SG-1.
Homecoming - Daniel Jackson rejoins SG-1 while Jonas Quinn returns to his homeworld to conduct negotiations with the neighboring nations.
Lost City, Part 2 - Fearing the latest Ancient Repository download will impair his judgment, Jack O'Neill gives up his command of the unit to Carter.
New Order, Part 2 - O'Neill becomes a Brigadier General, leaving SG-1 a three-person unit under the command of Samantha Carter.
Avalon, Part 1 - After SG-1 has gone their separate ways Colonel Cameron Mitchell takes command and begins interviewing potential teammates. But he is unimpressed by the candidates, and attempts to bring the others back.
Morpheus - Vala undergoes a psychological evaluation to determine her suitability for membership of SG-1.
Memento Mori - After several months as an unofficial team member, Vala is granted status a full-fledged member of SG-1.
Unending - SG-1 is trapped on the Odyssey in a time dilation field for 50 years, living out their lives together ... until Sam finds a way to reverse time and return them home.
Stargate: Continuum - When Baal changes the timeline, Sam, Cameron and Daniel return to Earth to find that the lives they knew are gone -- and SG-1 disbands for a year, until the Goa'uld's arrival brings them back together to set things right.