Exobiologists Magnus and Erin Hansen were the first humans to study the Borg up close, and along with their young daughter, Annika, were perhaps the first humans to be assimilated.
At least 10 years prior to the U.S.S. Enterprise-D's first encounter with the Borg, the Federation had some knowledge of the existence of the Borg, based on encounters with species who had been affected by them (such as the El-Aurians, whose homeworld was destroyed 90 years before). However, such knowledge was not made public among the Federation because information was too sketchy and unconfirmed to hold briefings with Starfleet personnel. (For example, there were descriptions of cube-shaped vessels, but no information on what Borg individuals looked like, other than rumors that they were cybernetically enhanced.)
Two of the people privy to these rumors were Magnus and Erin Hansen, who petitioned the Federation Council on Exobiology to let them travel deep into unknown space on the U.S.S. Raven to observe and study the Borg. Their petition was granted ca. Stardate 32611, in spite of Starfleet's concern about security issues, and the Hansens departed from Deep Space 4 toward the Delta Quadrant.
For eight months, the Hansens tracked nothing but stray readings and sensor echoes, and in the process of chasing their theories about the Borg, the unconventional scientists deviated from their flight plan, crossed the Neutral Zone and disobeyed a direct order to return, effectively burning their bridges with colleagues back home. But then they detected a transwarp conduit from which emerged a Borg Cube. The Raven was scanned by the Cube, but the Borg ship did not alter course, apparently considering the small vessel neither a target nor a threat. The Hansens tracked the Borg Cube through the relatively nearby region of space for three months, when the Cube finally entered a transwarp conduit again. The Hansens followed in its wake, and found themselves in the Delta Quadrant — the Borg's native territory.
The Hansens designed a variety of new technologies to allow themselves to study the Borg up close without being detected. They developed multi-adaptive shielding to make the Raven virtually invisible to Borg sensors, and a "bio-dampener" to camouflage a visitor on a Borg ship, by creating a field around the body that simulates the physiometric conditions within the vessel. Magnus periodically made "field trips" to the Cube they were tracking to observe first-hand the behavior and interactions of the drones; he even gave them nicknames such a "Junior" and "Needlefingers."
The Hansens studied the Borg in this way for over two years, collecting 10 million teraquads of data. But then a subspace particle storm damaged the Raven and caused its multi-adaptive shielding to go off-line for 13.2 seconds, long enough for the Borg to perceive the vessel as a threat. In spite of the Hansens' attempts to hide in a nebula and mask their warp trail, the Borg caught up with the Raven as it crash-landed on a Class-M moon orbiting the fifth planet of a yellow dwarf star in B'omar space. All three of the Hansens were assimilated into the Collective at that time, including the young girl, who became the drone designated as "Seven of Nine, Tertiary Adjunct of Unimatrix Zero One."
The Hansens' field notes, contained in 9000-plus log entries, were retrieved by the U.S.S. Voyager from the wreckage of the Raven. The crew later used that data to aid in their assault upon a Borg vessel to steal a transwarp conduit. It was during this assault that Seven of Nine was lured back to Unimatrix One by the Borg Queen, at which time she encountered her assimilated father, Magnus, in the Queen's lair. The Borg Queen vessel was later destroyed, but it is uncertain if the Magnus Hansen drone was aboard at the time.