A Game of Thrones Theme of Betrayal

A Game of Thrones is chock-full of betrayals, treachery, and abandonment. (Also conspiracies, subterfuge, manipulations… should we go on?). Even the people who are incredibly principled do their share of betraying. But remember that betrayals are different than lies (even king of principles, Ned Stark, notes, "We all lie" [23 Arya 2.63]). In order to betray someone, you have to have their trust first. So if there is a lot of betrayal in the world of A Game of Thrones, that means there's also a lot of trust. In a world where no one man can accomplish anything on his own, trust is hugely important; and that means betrayal is a major risk. And a major pain in the neck.

1. Which characters first come to mind when you think of betrayal? Does Martin use any particular techniques to describe these characters? Does he foreshadow betrayal or does it usually come as a surprise?
2. Do any of these characters betray themselves?
3. Are there any times in this book when betraying someone is the right thing to do? (For example, when Sam tells Jon's friends that Jon is running away, is that a betrayal?)