Seven of Nine was born as Annika Hansen, the daughter of two excentric exobiologists, Magnus and Erin Hanson. She was born in 2348, but because of her parents work, she was raised by her aunt, Irene Hansen, on Earth.
Major Story Arcs
Early Life and Assimilation
"Seven of Nine, Tertiary Adjunct of Unimatrix 01. But you may call me Seven of Nine."
Seven of Nine was born to parents Magnus and Erin Hansen. She was given the birth name, Annika Hansen. Her parents were exobiology (they studied non-human or alien organisms) who studied a then-unknown species known as Borg. When Annika was 4, they took her along with her for a long-term scientific mission to seek them out on-board their ship the USS Raven. For a couple of years, their research had gone without incident.
They had found and followed a Borg cube to the Alpha Quadrant. They had come up with some kind of shielding which prevented them from being detected. However when they encountered an ion storm, it struck The Raven which damaged their systems including the shielding. They tried to evade the Borg, but it was futile. The family was captured and assimilated. They became drones.
Borg Drone and De-Assimilation
For the next 18 years, Annika would be known as Designation: Seven of Nine, Tertiary Adjunct of Unimatrix 01. And like any other Borg drone, she would unwillingly assist in assimilation individuals and entire races, and if necessary, kill. She would while being in the collective hear the collective voices of billions, maybe trillions of drones in her head. It wasn't until the Borg's war with a mysterious race known only as Species 8472, the Borg designation for them. The race's true name was never revealed. The Borg attempted to invade their realm. But not only did Species 8472 fought back, they overwhelmed the Borg due to the fact they could not assimilate them. The Borg entered in an uneasy alliance with the lost ship, USS Voyager.
Annika or rather Seven would serve as kind of an emissary between the Voyager crew and the Collective during the brief, yet very destructive war. After they achieve final victory against Species 8427 thanks to the Voyager's assistance, they would betray the crew and attempted to assimilate them by using Seven of Nine. They put her down and disconnected from the hive mind.
Recovery and Return to the Alpha Quadrant
Her recovery would not be easy. It took her years to adjust to being an individual. However she proved invaluable members of the Voyager crew. Seven develops social skills and engages in a romantic relationship with Chakotay. With her help and a few events individuals, allies, and races they would assist, they found their way back home.
Myriad Universes - The Last Generation
In this alternate universe, Annika was never assimilated by the Borg. Instead, she is a member of Picard's resistance movement against the Klingons. When Picard learns that the universe is the way it is because of a time travelling lunitic, he decides to try to right the past. Annika is among a small group of rebels, led by Wesley Crusher, that decided to go against him.