According to a computer display in the episode "In a Mirror, Darkly", historian John Gill considered Archer "the greatest explorer of the 22nd century." The same display states that two planets were named after Archer: Archer IV and Archer's Planet.
Archer grew up with a distrust of Vulcans, since he perceived them as having held back Humanity's progress, particularly with regard to his father's warp five engine. It is strongly suggested in several episodes ("The Seventh", among others) that prior to joining Starfleet, he studied at and played water polo for Stanford University just south of San Francisco. (Starfleet Academy would not be founded until 2161.)
In Starfleet, Archer served as a pilot in the NX warp trials with A.G. Robinson, Duvall, and Gardner (all mentioned in the episode "First Flight"; it is assumed it is this Gardner who becomes Admiral when Admiral Maxwell Forrest dies in "The Forge"). Robinson pushed the limits of a test ship, the NX-Alpha, resulting in its destruction. The Vulcans recommended the warp trials end, which Starfleet agreed to until Charles Tucker III (who would serve as chief engineer under Archer) fixed the intermix ratios, and Archer and Robinson stole the NX-Beta, the second test ship, to prove its readiness. Although Archer was suspended for the act, it is believed his risk (and the fact it paid off) eventually secured his role as Captain of Enterprise, Earth's first warp five starship.
In addition, Archer learns the duties of captain include being a diplomat. During Seasons 1 and 2, he is somewhat uncomfortable with the role, especially in the episode "A Night in Sickbay" when his pet beagle, Porthos, contracts a deadly illness on an alien world.
While exploring, Archer becomes an enemy of the Klingons. In a dispute with the Klingon Empire in 2152, he is convicted and sentenced to exile on Rura Penthe, even though he is innocent of the charges and despite the Klingons having acknowledged his previous service to the Empire. With his escape, a bounty is put on Archer's head and tensions with the Klingon Empire increase.
Also during this period, Archer has the distinction of making Earth's official first contact with dozens of alien races, including the Andorians, Axanar, Suliban, Tandarans, Tellarites, Tholians, Xindi, and Romulans (although this is not a face-to-face contact).
As the Temporal Cold War continues, we also meet Daniels, a character whose purpose seemingly is to safeguard Archer in particular and Enterprise in general. Daniels' comments are that Archer will be the man who helps to form the United Federation of Planets, and it becomes apparent by the third season that Daniels is representing the Federation throughout the Temporal Cold War.
While on his mission to locate the Xindi, Archer is briefly transformed into a member of the extinct Loque'eque by a mutagenic virus. Later, he is infected by subspace parasites, creating an alternate timeline in which the Enterprise's mission fails and Earth is destroyed. With the help of Daniels, Archer, along with T'Pol, travels back in time to 2004 Detroit to prevent the release of a Xindi-Reptilian bio-weapon.
Archer is also involved in one of the first, and possibly most significant, treaties yet, being asked to escort Gral, the Tellarite ambassador, to the Tellarite-Andorian negotiations. En route, he and his crew run into the Andorian Shran, a long-time friend/enemy/ally. During his stay, Romulans attack and cause the fragile alliance to crash to a halt. In the mix-up, a Tellarite kills Shran's lover Talas, and Shran avenges her death by asking the Tellarite who killed her to fight to the death. In an attempt to protect the fragile peace treaty, Archer takes the challenge instead and Shran is incapacitated (but not seriously hurt). The alliance remains intact, and soon after, evolves into the United Federation of Planets. ("Demons", "Terra Prime", "These Are the Voyages...")
Episodes in the first and second seasons seemed to suggest that Archer and T'Pol had the potential to become more than just close friends. Archer is openly jealous when a Vulcan suitor pursues T'Pol in the episode "Fusion", and insists the Vulcans won't take something away from him that's important ("Shadows of P'Jem") — meaning T'Pol. He assists her in finding help with her Pa'nar Syndrome, and indicates he is happy she will be staying aboard in the episode "Stigma", and many other instances. However, it appears Archer's drive to complete the Xindi mission and save Earth diminished this possibility.
There has also been evidence of extreme sexual tension between T'Pol and Captain Archer, as seen in the episode "Shadows of P'Jem" where T'Pol and Archer are tied up together and end up in embarrassing and sexually stimulating positions as they try to escape the bonds. This was all accompanied by intense staring, slight moaning and heavy breathing.
In the alternate timeline of Twilight, T'Pol becomes Archer's caretaker for more than a decade after subspace parasites rob him of his ability to form long-term memories after the point of the incident; the question of how far their relationship had progressed in this timeline goes unanswered, but it is made clear that some bond of love existed by that point, albeit somewhat one-sided as this alternate future Archer is unable to retain memory of it. It remains to be seen whether anything close to this occurs in the "real" timeline, even though the writer of Twilight indicated in Star Trek Communicator that eventually Archer and T'Pol would marry in the real timeline, a point some think was in jest. The series finale gives no clue as to whether this outcome actually occurs, but certainly implies a much closer relationship than previously seen and leaves it open for the possibility.
Archer's fate is revealed in the episode "In a Mirror, Darkly, Part II" when a computer information screen aboard the 23rd century Starfleet vessel USS Defiant is briefly visible. According to the computer profile, Archer was an Admiral and Chief of Staff at Starfleet Command at the time of his retirement. He later went on to serve as ambassador to Andoria from 2165 to 2175. From 2175 to 2183, Archer served as a member of the Federation Council, followed by eight years as Federation President (2184-2192). He was also an honorary member of the Andorian Imperial Guard.
Unused artwork shows that Archer dies peacefully in his sleep at his home in Upstate New York in 2245, exactly one day after he attends the commissioning ceremony of the USS Enterprise (NCC-1701). (This is the first canonical confirmation of the date the NCC-1701 was launched.) However, this computer display gives 2160 as the year Archer's captaincy of Enterprise came to an end, which is contradicted by the 2161 date given in "These Are the Voyages..." A reason for this inconsistency could be the fact that the scenes depicted in "These Are the Voyages..." were a holographic recreation experienced by William Riker in the 24th Century.
Porthos was portrayed by a male beagle named Prada in Season 1. Afterwards, he was played by two female beagles, Breezy and Windy, although the character of Porthos remained male. Prada also portrayed the character Lou in the film Cats & Dogs.
Archer cares very much for Porthos. In the pilot episode, Travis Mayweather says Archer won't use the transporter for himself and certainly not for his dog. In "A Night in Sickbay", Porthos nearly dies when he contracts a deadly pathogen on the Kreetassan homeworld, but is saved when Phlox transplants a gland from a chameleon-like creature.
Although Porthos isn't the first domesticated pet to be featured in a Star Trek series (Data owned a cat, Spot, in Star Trek: The Next Generation), Porthos has the distinction of being the first pet to maintain an ongoing presence in the series, and even - as illustrated above - become the focus of an episode.
In the Mirror Universe depicted in "In a Mirror, Darkly", Porthos is a Rottweiler. According to the episode's podcast on Startrek.com, the dog that portrayed the mirror Porthos was known on set as an even bigger "baby" than the dogs which have played the regular Porthos. Episode writer Mike Sussman noted that the animal was "The sweetest dog I have ever met."
In the episode "Acquisition", Porthos was interrogated by a group of Ferengi pirates while the rest of the crew were incapacitated, but the aliens' universal translator could not decipher his barking. The pirates didn't know what to make of the dog, even speculating that he was perhaps food.
The mirror Archer, like most characters in the Terran Empire, was treacherous, cunning, and scheming. He led a mutiny against Forrest and took over Enterprise. However, with the help of T'Pol and other Vulcans, Forrest was freed and retook the ship. Archer surrendered, but had locked the ship's navigation controls so its heading could not be altered. His reason for the mutiny was brought to light as he had been informed about a ship that seemed to be from another dimension. With the ship's course unable to be changed and Starfleet now intrigued by what Archer had become aware of, Forrest was ordered to investigate. On arrival, they discovered the USS Defiant, a Starfleet ship from the normal universe.
Archer led a team to take control of the Defiant while Enterprise was destroyed by the Tholians. He and his team, plus survivors from Enterprise, discovered Defiant is not only from another dimension, but the future and that the alternate dimension never had a Terran Empire. After successfully crushing a rebellion against the Empire, Archer attempted to take the futuristic vessel to Earth where he would proclaim himself Emperor. However, before he could do so, he was killed by his universe's Hoshi Sato, who poisoned him and took the ship and (we are led to believe) the Terran throne as well for herself.