The Borg first appear in the Star Trek: The Next Generation episode “Q Who.” Q sends the Enterprise-D far across the galaxy to teach Picard that the Federation is not prepared for every danger beyond its borders.
The crew encounters a Borg cube and initially tries to communicate. The Borg show no interest in negotiation; they scan the ship, disable its defenses, and begin cutting into the saucer section. An away team also discovers how efficiently the cube’s drones operate as a single collective intelligence.
The Enterprise cannot outrun or defeat the cube. Picard finally admits that he needs Q’s help, and Q returns the ship to its original location. Guinan warns that the encounter has alerted the Borg to the Federation’s existence, setting up the threat that dominates “The Best of Both Worlds.”
“Q Who” is sometimes confused with “The Best of Both Worlds,” which made the Borg a central continuing enemy and introduced Picard’s assimilation as Locutus. However, “Q Who” is the episode that first puts the Borg on screen.