First introduced in Star Trek: The Next Generation season 2, the Borg are Star Trek's biggest bad because of one vital change made to the early concept of an unbeatable enemy. After the introduction of the Ferengi in TNG season 1 failed to establish the profit-obsessed aliens as Star Trek's new big bad, the writers' room went back to the drawing board. The Star Trek: TNG season 1 finale, "The Neutral Zone" was designed to tease the arrival of a deadly new enemy in season 2. However, complications caused by the 1988 writers' strike meant that this tease was never properly paid off on-screen.
The 1988 writers strike delayed the Borg's Star Trek debut but this extra time allowed for a considerable rethink as to the nature of an unbeatable enemy. Writer-producer Maurice Hurley originally had a very different concept for the new Star Trek enemy that would terrorize the crew of the USS Enterprise-D. Like the Borg, this new species would be driven by motivations beyond human comprehension, but unlike the Borg, it's hard to see Hurley's original concept becoming as impactful on the Star Trek franchise as the Borg Collective was.
