Crew unlocking condition ideas?

So this is not an update quite yet but I'm merely looking for some ideas. I'm currently in the works of adding some actual permanent progression/unlocks to the game. So if you've got any good ideas on how to unlock some specific crew members to be your starting members, post in the comments.

The conditions shouldn't be anything too difficult or rare but not something that'd always unlock when you acquire said crew member. And of course would be good if they were actually related to the target crew member in some way or another.