4.Who left humanity behind:
Fain is the likely suspect. Though I did notice that strictly speaking the sentence only says that the creeper has left humanity behind. It does not say "one who has left _his_ humanity behind". So in theory this could be someone very human that is on a suicide mission to the blight with no intention of ever leaving the blight and returning back to "humanity", such as a male Aiel channeler who has yet to learn that saidin is clean. Or somesuch. Though in truth this is wordplay and Fain is the likely suspect, unless someone is trying to deliberately trick us.