There are two main types of antagonists in Star Trek. Sometimes an entire alien race, such as the Borg, the Romulans or the Dominion, becomes the sworn enemy of the United Federation of Planets, kept at a distance via treaties, neutral zones or wormholes. Occasional descents into all-out war are a clear and present danger.
The other flavor is the solo villain, a species of independent combatants who've generally developed some kind of beef with Starfleet, and will stop at nothing to ensure their destructive schemes — which may or may not have galactic significance — come to fruition. These grandstanding lone wolves often have a penchant for supervillain-style monologues, and are more traditionally associated with the Trek movies than the TV shows.
