Federation science vessel, registry no. NAR-32450, manned by exobiologists Magnus and Erin Hansen, along with their young daughter, Annika — the first humans to study the Borg up close, and perhaps the first 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 Raven 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 Raven followed in its wake, and found itself 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 Raven itself was partially assimilated by Borg technology, and was left emitting a resonance signal — a "homing beacon" which 18 years later inadvertently summoned the Seven of Nine drone (who by that time had been separated from the Collective and was serving aboard the U.S.S. Voyager). Seven of Nine had been experiencing strange visions involving a threatening black bird — a raven — which turned out to be a subconscious metaphor for the trauma Annika Hansen experienced when she and her parents were kidnapped from their vessel and assimilated.
Because Seven of Nine had violated B'omar space in order to respond to the homing beacon, the B'omar fired upon the Raven wreckage while she and Voyager crewmate Tuvok were inside it. Seven and Tuvok escaped from the vessel and were beamed up by Voyager just as the Raven was finally, completely destroyed. In addition to rescuing the crewmates, Voyager also managed to retrieve the Hansen's field notes from the ship (contained in 9000-plus log entries), which the crew later used 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.