Colonel Samantha "Sam" Carter, USAF, is a fictional character in the Canadian–American military science fiction Stargate franchise. Played by Amanda Tapping, she appears in all three shows in the franchise: Stargate SG-1, Stargate Atlantis, and Stargate Universe. She was a main character in all ten seasons of Stargate SG-1 (1997–2007). Following a recurring role in Stargate Atlantis for three seasons (2004–07), Carter became a main character in Season 4 of Atlantis (2007–08), and also appeared in the 2008 direct-to-DVD SG-1 films Stargate: The Ark of Truth and Stargate: Continuum. Amanda Tapping accepted a starring role in Sanctuary and appears in only the first and last episodes in Season 5 of Atlantis (2008–09). Carter also appears in two episodes of Season 1 of Stargate Universe.

Captain Samantha Carter first appears in "Children of the Gods", the pilot episode of Stargate SG-1, as a United States Air Force captain who joined the fictional SG-1 team under the command of Colonel Jack O'Neill. After being promoted to major in Season 3, Carter remains O'Neill's second-in-command until her promotion to lieutenant colonel early in Season 8, at which point she assumes command of the SG-1 team and O'Neill is promoted to brigadier general in order to lead Stargate Command. Between Seasons 8 and 9 of SG-1, following the defeat of the Replicators and downfall of the Goa'uld system lords, she accepts a position as Head of the Stargate Research and Development Program, based in Nevada. She is engaged in deep-space research when the Ori emerge. Upon her return to Earth, she is reassigned to SG-1, now under the command of Lieutenant Colonel Cameron Mitchell. Following the defeat of the Ori in Stargate: The Ark of Truth, Carter is promoted to full colonel and appointed as commander of the Atlantis expedition early in Season 4 of Atlantis. Carter is later given command of the Daedalus-class ship, the George Hammond.

Unofficially in the online game Stargate: Resistance, it is implied by visual screenshots showing a general's office with her name on the desk label that she eventually succeeds Major General Hank Landry as commander of the SGC, implying an offscreen (non-canonical) promotion to brigadier general.

Overall, Carter is the character with the most appearances across the Stargate franchise, though ranking as second-most — behind Teal'c — in the series Stargate SG-1.

Before the present-time events of Stargate SG-1, Samantha Carter worked at the Pentagon for several years, trying to get the Stargate operational. She has a Ph.D. in theoretical astrophysics and "logged over 100 hours in enemy airspace" during the Gulf War. She is the daughter of Major General Jacob Carter, and has a brother named Mark. Her mother died in a car accident when she was a teenager.

Holding the rank of captain, Samantha Carter joins the SG-1 team in the pilot episode, "Children of the Gods". She comes under the temporary control of the Tok'ra Jolinar in season 2 and retains many of her memories, leading to an alliance with the Tok'ra against the Goa'uld. Carter's brief merging with Jolinar also assists her in detecting a Goa'uld presence and using certain Goa'uld technology. Carter is promoted to the rank of major early in season 3. When an advanced lie detector shows they are concealing something in early season 4, it forces Carter and her superior officer, Colonel Jack O'Neill, to admit that they care for one another "a lot more than [they're] supposed to". In Exodus (season 4), Carter uses a stargate to destroy a star by dialing the gate on P3W-451, the planet being consumed by a black hole (originally discovered in A Matter of Time), and launching the active stargate into the nearby star; the resulting imbalance in mass causes the star to go supernova and destroy Apophis's fleet.

Trapped on board the Earth ship Prometheus in season 7's "Grace", Carter realizes that her feelings for O'Neill stop her from exploring other romances. Two episodes later in Chimera, Carter begins dating her brother's friend Pete Shanahan, but Pete disrespects her privacy and the confidential nature of her work. Pete gaslights her and stalks her until she is forced to disclose her job to him. In the season 8 premiere, "New Order", Carter gets captured by a humanoid Replicator named Fifth she had first encountered in season 6's "Unnatural Selection". Fifth eventually releases her, but keeps a replicator copy of her, known commonly as 'RepliCarter'. Upon O'Neill's promotion to brigadier general in the same episode, he promotes her to lieutenant colonel. Carter assumes command of the SG-1 team, which includes the de-ascended Daniel Jackson, the alien Teal'c, and herself. Shortly after the death of her father in late season 8, Carter breaks up with Pete and goes fishing with Jack, Daniel, and Teal'c to celebrate the defeat of the System Lords.

Season 9 reveals that Carter left SG-1 to work at Area 51 after the collapse of the Goa'uld power structure. After Lieutenant Colonel Cameron Mitchell assumes command of SG-1, General O'Neill orders Carter to assist SG-1 on a mission concerning the new Ori threat. Carter officially rejoins SG-1 in the season 9 episode "Ex Deus Machina". Samantha Carter appears in the 2008 direct-to-DVD films Stargate: The Ark of Truth and Stargate: Continuum.