I was just browsing the thread below this which indicated that Jason Todd would be a contender for the Batman mantle if it were to become available which made me wonder:

When did Jason become a good guy?

The last I read about him, I believe it was in a few issues of Nightwing (probably a year ago, maybe longer), he was somewhat crazy and he was busy trying to mess up Dick's life. Also, how did he come back to life?

Also:

How did Jason die? Did Joker beat him to death with a crow bar? or did he die in an explosion while trying to save his mom? (which is what I seem to recall reading somewhere).

Thanks.