Romulans

The Romulans are one of the most prominent villains of Star Trek, one of the few alien races in the series that has remained hostile towards the Federation, having never truly been defeated nor allied.

The Romulans have a striking resemblence to Vulcans but embrace a power-hungry philosophy centred on military aggression and imperialism, they have been behind the scenes in many of Star Trek's more prominent conflicts and their animosity with the Federation has lasted generations.