Question: when are the borg introduced?
Answer: Borg appearances. The Borg were introduced on syndicated television on May 8, 1989, in the Star Trek: The Next Generation episode "Q Who?", and rose to further prominence in the famous two part cliffhanger "Best of Both Worlds, Part I", which aired on June 18, 1990, with the sequel airing on September 24, 1990.