Perhaps the most significant villains of Star Trek: The Next Generation and its era of the franchise were the Borg. A hive-mind collective, their only goal was conquest and assimilation of "biological and technological distinctiveness." Yet, Star Trek: First Contact revealed the Borg collective had a Queen, even though she never appeared in The Next Generation. Yet, the successive stories featuring the character explain why it took so long for her to surface.
Source：https://www.cbr.com/star-trek-theory-borg-queen-the-next-generation/
