The Octanti (known to the Borg as Species 6339) were a technologically advanced sentient humanoid from the Delta Quadrant. They originated from Grid 124, Octant 22-theta, circa 50,000 light-years from Earth. Their ships tended to be well-armed, with one type being equipped with twenty-two phaser cannons on the aft section alone. (VOY episode: "Infinite Regress")
In 2371, the Octanti made first contact with the Borg Collective. The Borg began assimilating the Octanti, and the Octanti resisted. However, despite the resistance, billions of Octanti were assimilated.
On stardate 52356.2 (May 11, 2375), they made first contact with the Federation when they encountered USS Voyager. By this time, 11 billion Octanti had been assimilated by the Borg. Voyager asked the Octanti to help one of its crewmen, the former Borg drone Seven of Nine. The Octanti had allowed some of themselves to be assimilated by the Collective to infect a vinculum, which they hoped the Borg would retrieve to spread the disease unwittingly. Captain Kathryn Janeway eventually persuaded Ven to aid them. Voyager learned their remaining vessels were well-armed with phaser cannons. (VOY episode: "Infinite Regress")
In early 2410, Klingon Imperial Intelligence officer Galera briefed Klingon Defense Force commanders on the Octanti by sharing Octanti Intelligence File 3241-M as part of Operation Delta Rising. The file stated only a handful of Octanti escaped from assimilation. Only those on the starships of the Octanti fleet survived. By the early 25th century their numbers were still dwindling but the Octanti were committed to kill all Borg, including liberated Borg. Galera concluded an alliance with the Klingon Empire was possible as long as the Klingons would not interfere with the Octanti's mission. (ST video game: Star Trek Online)
The Octanti were first encountered battling the Borg Cooperative in the Parein system, where a member of the Alpha Quadrant Alliance disabled ships from both sides to get them to talk. Despite the Cooperative's insistence that they were not the bad guys, the Octanti refused to believe it and still declared all Borg enemies. (STO mission: "With Friends Like These...")
They were encountered again in the Brothra system after a fight disabled a number of their ships. When the Vaadwaur Supremacy sprung a trap using the disabled ships, the Borg Cooperative aided the AQA member in protecting the Octanti. Awed by their actions, the Octanti, including Captain Xar, vowed to get the leaders to see otherwise. However, it was revealed that they considered the actions of the few insignificant. (STO mission: "Know Your Enemies")
They were encountered once more in the Russan system, where Seven of Nine and the Cooperative still sought the aid of the Octanti. Ambassador Rerrick still refused to listen. However, when his brother, Meshk, appeared to him, Rerrick was shocked that his brother was still alive and among the Cooperative. However, he still had the anti-Borg virus within him and it was causing havoc on the Borg Cube he was in. The Cooperative, Octanti, and the AQA member were able to disable the Cube while Rerrick disabled the virus. Moved by the revelations, Rerrick vowed to see that the Cooperative were considered allies and that their lost members were with them, though many Octanti still refused to work with them. (STO mission: "Alliances")