I just realized the achievement title was a pun on "Justice." The achievement says to "Listen to all of the Tyrael's conversations."
Because Tyrael is always running off and disappearing, making it hard to talk to him, it seems like it would be easy to miss a lot of these, so I'd like to know when Tyrael's conversations first become available and if and when they become unavailable.
Best Answer
Tyrael/The Stranger will even talk to you after you kill the final boss, but conversations with him are often in small spurts.
Act I
Act II
Act III
Act IV