The Dominion - a forbidding partnership of alien races based in the Gamma Quadrant - are as ominous as their name suggests. First alluded to in the Deep Space Nine episode 'The Rules of Acquisition' and introduced in the 1995 episode 'The Jem'Hadar', The Dominion epitomise the series' often pessimistic and determinedly unique Trek style.

Established by the mysterious race known as the Founders 2000 years before the Deep Space Nine series began, the Dominion are without doubt one of the Federation's most powerful and politically complex enemies.

Dedicated to expanding their planetary empire, the Dominion use Jem'Hadar soldiers to mercilessly enforce their rule. The Founders - revealed to be shape-shifters of the same race as DS9's security chief Odo - have been attempting to infiltrate the Alpha Quadrant in the lead-up to a full-scale Dominion invasion. The final episode of Deep Space Nine, recently broadcast in the US and the subject of rapturous reviews, apparently goes some way towards resolving the Dominion/Federation war.

The Dominion have typified Deep Space Nine's willingness to experiment with elaborate, multi-layered storylines. The political machinations of the Dominion, the Federation, the Cardassians and the Romulans has now progressed over five seasons, proving that Deep Space Nine was not designed for viewers with short attention spans.

It is perhaps hard to imagine Gene Roddenberry sanctioning such a fatalistic and refreshingly oblique concept as the Dominion. Yet it has paid off. 'The Quickening', an episode dealing with the catastrophic effects of a plague the Jem'Hadar have unleashed on a planet that resisted Dominion rule, is arguably one of the best examples of how Deep Space Nine's departure from the typical Trek pattern can produce great TV.

Key Deep Space Nine Dominion Episodes: 'the Jem'Hadar', 'the Quickening' 'Shadowplay', 'The Die is Cast', 'By inferno's Light', 'What You Leave Behind'.