The Arkonians were a species of humanoid reptilian native to the Alpha or Beta Quadrant. The Arkonians were warp-capable since the 2050s. Soon after, Vulcans established first contact with them. (ENT episode: "Dawn") Vulcans generally considered the Arkonians to be aggressive, dangerous and irrational. (ENT - The Romulan War novel: To Brave the Storm)
As reptilians, the Arkonians did not have sweating glands, and their cellular structure was not capable of handling rapid temperature changes. They had a scaly skin with ridges running along the sides and top of their faces.
Biologically, Arkonians were distinct from other species by their non-water based hydration system. Instead, Arkonians relied on drinking a brown liquid, tarratt-aash, which was unpalatable to other species, including Humans.
By November 2163, the Arkonians were still manufacturing and marketing their starships to several species, including Tellarites. Arkonians ships with the colors and alterations were favored by the Tellar Space Administration. (ENT - Rise of the Federation novel: Tower of Babel) Their starship types included the Arkonian destroyer, which was equipped with combat-worthy shuttles. (ENT episode: "Dawn")
After the Arkonians achieved warp capability in the 2050s, they made first contact with the Vulcans. The Arkonians distrusted the Vulcans and relations cooled. After the Vulcans were recalled, the relationship between them and the Arkonians remained rocky. (ENT episode: "Dawn")
In late 2152, the Arkonians made first contact with the United Earth Starfleet vessel Enterprise (NX-01). An Arkonian shuttle shot down one of Enterprise's shuttlepods over a moon in a recently annexed system. The Arkonian shuttle crashed as well, forcing its pilot and Commander Charles Tucker III to work together to survive in the hot environment. Meanwhile, Captain Jonathan Archer convinced the commanding officer of the Arkonian mothership to cooperate in finding their missing crewmembers. The Humans and Arkonians parted on better terms than the Vulcans had managed to achieve in a century. (ENT episode: "Dawn")
On December 11th, 2156, during the Earth-Romulan War, Captain Archer joked with his first officer T'Pol how Starfleet may send him to expand his charm offensive to gain allies for Earth to include the Arkonians, after his failed attempt to convince the Vissians. T'Pol detected the sarcasm. (ENT - The Romulan War novel: To Brave the Storm)
On March 14th, 2163, Admiral Archer and Captain T'Pol of USS Endeavour discussed how the young United Federation of Planets had to avoid appearing threatening towards aggressive neighbors, including the Arkonians and Tandarans. (ENT - Rise of the Federation novel: A Choice of Futures)