Now that we've seen all three Walkers on screen, I'm struck by the extent to which they parallel the three virtues represented by the Swords.
Hope: B4 -- I AM FEARGIVER, HOPESLAYER!
Faith: BS -- Treachery is the very definition of broken faith.
Love: BH -- the mastercraftsman of death (hate or indifference?)
I'm not quite sure how to characterize Behind. In Blood Rites, we get: "O Lord of Slowest Terror! May your right arm come to us! Send unto us your captain of destruction! Mastercraftsman of death! ... He Who Walks Behind!"
(That's also a really fun scene to reread now, since it's the moment when Lara realized that Harry is much more than he appears. "You've made me the cat's-paw for you, Dresden... Clearly, I underestimated you." "Don't feel bad," I said. "I mean, I look so stupid." -- with hindsight, that might count as their "meet cute"... *shudder*)
In Ghost Story, when we really see Behind in action, aside from Harry's fear the two emotional descriptions we get are the way Behind casually turns Stan into three piles of meat... and the righteous fury Harry feels in response.
I'm not sure whether Behind is meant to represent utter indifference as the opposite of Love, or hate and rage as the opposite of Love.
In any case, I'm expecting a scene in Empty Night, final book of the Dresden Files (not counting the Maggie outriggers.) -- the three Knights of the Cross charging into battle against the three Walkers, although I'm not sure whether Harry will be carrying Amoracchius and getting his final showdown with Behind or whether he'll be facing off against the Lord of Slowest Terror.