Father of Samantha and Mark Carter, Jacob was a longtime member of the Air Force, retiring as a two-star general. Jacob soon learned that he was afflicted with lymphoma and accepted an offer from the Tok'ra to live on by becoming host to one of the resistance movement's oldest and wisest leaders, Selmak.
Jacob believed his daughter's greatest dream was to become an astronaut, and he made it his business to make certain she followed her dream. He took offense when she rejected his offer for help in getting into NASA, not knowing the true nature of her work on the Stargate program. He could not believe she would prefer being locked inside Cheyenne Mountain analyzing "deep space radar telemetry."
When General Hammond, Sam, and the Tok'ra offered blending with Selmak, Jacob could not believe what he was hearing -- but was eventually willing. He traveled through the Stargate and became a host joining the Tok'ra movement and also taking the title of liaison between the Tok'ra and Tau'ri. Since blending, his perceptions of the universe have forever changed. Jacob has become far wiser and less stubborn, though also more arrogant than Sam would have wanted.
However, he continues to come to the aid of Earth and the S.G.C., while taking on daring missions to defend the Tok'ra from the Goa'uld. While the S.G.C.'s relationship with the Tok'ra has been occasionally rocky, Jacob has always been their advocate and ally.
Secrets - Samantha discovers that her estranged father, a retired Air Force general, has terminal cancer.
The Tok'ra, Part 1 - SG-1 is trapped offworld by a faction of rebel Goa'uld, while Carter's father lays dying on Earth.
The Tok'ra, Part 2 - Jacob's life is saved when he agrees to become joined with the Tok'ra Selmak, making him Earth's official liaison to the Tok'ra -- the S.G.C.'s new ally in the fight against the Goa'uld.
Show and Tell - Jacob returns to Earth to help defend the SGC against a rebel faction of Re'tu, who are trying to destroy the Goa'uld by wiping out all possible hosts.
Seth - Jacob helps SG-1 track and kill the Goa'uld Seth, who has been hiding on Earth for thousands of years. Prompted by Selmac, Jacob patches things up with his estranged son, Mark.
Jolinar's Memories - Jacob his captured by the powerful rebel Goa'uld Sokar, and imprisoned on the hellish moon of Netu. SG-1 attempts a rescue.
The Devil You Know - Jacob is rescued from Netu by SG-1 and the Tok'ra, having relayed important information about Sokar's plans to attack the System Lords.
Tangent - Sam and Daniel find Jacob preparing to destroy a Goa'uld naquaada mine, and enlist his help to rescue Teal'c and Colonel O'Neill -- who are trapped in a death glider leaving Earth's solar system.
The Serpent's Venom - After a short visit to Earth, Jacob and SG-1 are sent to sabotage an alliance between Apophis and Heru-ur.
Exodus - Using a Goa'uld mother ship taken from Cronus, SG-1 and Jacob blow up the Vorash star and wipe out much of Apophis's fleet -- but find themselves 125 years' travel from Earth.
Enemies - Jacob and SG-1 battle Replicators, Apophis and a brainwashed Teal'c to get their ship back home, and barely escape with their lives.
Summit - Jacob takes Daniel undercover on a Tok'ra mission to kill seven key System Lords at a summit on board a space station.
Last Stand - Jacob and Daniel's plan fails when Jackson is discovered, and the two return to Revanna to find the Tok'ra base destroyed.
Meridian - When Daniel is exposed to a lethal dose of radiation, Jacob arrives to try and save his life with a healing device -- but Daniel asks him to let him go.
Descent - SG-1 and Jacob investigate a seemingly abandoned Goa'uld mothership that has arrived in Earth's orbit, but a group of stow-aways crash the vessel into the ocean.
Allegiance - At the SGC's secret alpha site, Jacob must help SG-1 keep the Tok'ra and rebel Jaffa from killing each other -- in the midst of attacks by an invisible enemy.
The Changeling - As Teal'c and Bra'tac lay dying with no Goa'uld symbiotes, Jacob arrives at the S.G.C. to offer the drug tretonin, which can save their lives.
Fragile Balance - Jacob/Selmak arrive to render his assistance to the S.G.C. when a teenage boy shows up claiming to be Jack O'Neill -- but who is dying of genetic degradation.
Evolution, Part 1 - Jacob arrives with Selmak to analyze the super-soldier.
Evolution, Part 2 - Jacob/Selmak use the Kull warrior's armor to penetrate the Stargate forcefield on Tartarus, disabling the planet's sensors to allow the rest of the team to infiltrate Anubis's secret base.
Death Knell - Jacob aids in the construction of a weapon that can take down a Kull warrior. He also soon learns that the Tok'ra -- even the High Council, of which he is a member -- don't trust him as much as they once did, fearing that Selmak's Tau'ri host is having too great an influence over the symbiote.
Reckoning part 1 - Jacob/Selmak arrives through the Earth gate bearing stolen Tok'ra technology and a warning about the Replicators.
Reckoning part 2 - Jacob/Selmak helps Samantha activate the Dakaran super-weapon and eradicate the Replicators, but gets hurt in the process.
Threads - Jacob admits to Sam that Selmak is dying and has been for some time and it's now too late for the symbiote to save it's host.