I'm going to kick off this series with the Sontarans. That's partly because they've just been heavily featured in a new episode as I write this, but also because they are one of the races with the greatest potential for stories. They could even be adapted for other SF settings with a few serial numbers filed off. For that matter, they would make decent player characters, but I'm describing them here only as opponents since player rules would involve game balance considerations beyond the scope of these posts.
To begin with, let’s list the available source material, then look at what we know about this particular race.

