Star Trek: 10 Alien Races That Only Appeared Once
8. Krenim
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Can we class this as one entry or do the Krenim turn up multiple times?
Episode-wise it's a double header but a single story, the landmark Year of Hell. The Krenim had of course been mentioned in season three's Before and After with one of their ships being seen however, we didn't get to see a member of their race as we do here.
Kurtwood Smith's Annorax is one of Trek's quintessentially flawed opponents. I don't say villain since his mindset is not one of destruction but of restructuring to a "better time". One where his wife is alive and the Krenim Imperium is in a healthy state of expansion.
But with the Krenim themselves fans had a fascinating race which they saw evolve, step back, turn around, move forward over just two hours. The audience saw multiple stages of their expansion or collapse thanks to Annorax's interference.
Their weaponry was stunning, utilising temporal abilities against which Voyager struggled to defend. Having them back might have seemed a weak option since the thing that gave them their unique angle on the show, the Weapon Ship, was obliterated thanks to Janeway's careful driving.