>>213854982
Scorpius, Stark, Braca, and Chiana. All of them more or less acted their way to main character status.
It's one thing I like about season one; you can see the plot hooks that were being set up that were tossed away when they realized what they had in the actors.
There's hints about a relationship between Aeryn and D'Argo as well as between Zhan and Crichton; that falls away as they realized "Oh, Ben Browder and Claudia Black have such onscreen chemistry together that the problem is explaining why they aren't together." Frankly I'm still amazed they were both married to other people before, during, and after the run of the series. Browder's wife shows up at least three times in minor roles (Any short squeaky alien is probably her), and I'm pretty sure it's because she watched one episode and decided she needed to be on that set.
Likewise the Nebari as long term antagonists. Wayne Pygam acted them into irrelevance with Scorpius.