The Octanti (known to the Borg as Species 6339) were a technologically advanced sentient humanoid from the Delta Quadrant. They originated 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, over 11 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 are first encountered battling the Borg Cooperative in the Parein system, where a member of the Alpha Quadrant Alliance disables ships from both sides to get them to talk. Despite the Cooperative's insistence that they are not the bad guys, the Octanti refuse to believe it and still declare all Borg enemies. (STO mission: "With Friends Like These...")
They are encountered again in the Brothra system after a fight disabled a number of their ships. When the Vaadwaur Supremacy spring a trap using the disabled ships, the Borg Cooperative aided the AQA member in protecting the Octanti. Awed by their actions, the Octanti there vow to get the leaders to see otherwise. However, it's revealed that they consider the actions of the few insignificant. (STO mission: "Know Your Enemies")
They are encountered once more in the Russan system, where Seven of Nine and the Cooperative still seek the aid of the Octanti. Ambassador Rerrick still refuses to listen. However, when his brother, Meshk, appears to him, Rerrick is shocked that his brother is still alive and among the Cooperative. However, he still has the anti-Borg virus within him and its causing havoc on the Borg Cube he's in. The Cooperative, Octanti and the AQA member are able to disable the Cube while Rerrick disabled the virus. Moved by the revelations, Rerrick vowed to see that the Cooperative are considered allies and that their lost members are with them, though many Octanti still refuse to work with them. (STO mission: "Alliances")