Can you refresh my memory? Who were the other three? I remember Nazgrim, but the others are escaping me

1. Nazgrim
2. Thoras Trollbane
3. ???
4. Tirion ‘Tyrion’ Fordring

We’re not really sure who the third one is yet. I suppose there’s also a slim possiblity that Tirion isn’t the fourth, but then why are we raising him?