Person: The Father Office: King Atonement motif: Christus Victor
Person: The Son Office: Priest Atonement motif: Substitution
Person: The Holy Spirit Office: Prophet Atonement motif: Revealer (commonly called moral example)
I identify the Father with king because he is he fount of divinity and therefore divine sovereignty which the other two persons of the Trinity derive from him (obvious, by this I am not suggesting subordinationalism here!). The Son is the priest, because just as the High Priest/Adam received all things from the God their vocation was to return them to God through a vocation of sacrifice. So too the Son from eternity receives all things from the Father in an act of eternal begetting, in order return his being to the Father in the form of the breathing forth of the Holy Spirit. The Holy Spirit is the agent of prophecy- so that one pretty much self-explanatory.
Update: To clarify the last view of atonement, I call it "Revealer" because I don't want to suggest that Christ's role as prophet primarily has to do with the law (as moral example implies). It is correct to say that Christ preached both law and gospel, but Christ's primary function is to reveal and deliver the gospel.