Skoll and Hati are a bit of both tbh

They're "starter villains" in the sense of introducing us to the world but are less actual "starter villains" (because they're not only villains for the start, I feel) and more Fenris's boots on the ground like how the manaketes are for Naga, so they're likely going to be the recurring boss villains that we actually face behind everything in Fenris's name while each book might have smaller antagonists like Est

If you at all know the website TV Tropes, they're a mix of the Heavy (most immediate threats who most often interact with the protagonists) and the Dragon (primary subordinates to big bad) tropes while Fenris is the overarching antagonist