The Man is someone trying to fulfill his own bargain.He wants something big, something huge...and so he has to fulfil the role of the bargain-maker until he can find another replacement.
The Man helped with the Curiosity probe.Curiosity landed on Mars on August 6th. Season 2 started on August 6th. Coincidence? That's why this is WMG ;)
Doris is like The Man.The Man is as close as we've seen to being rattled when Doris re-appears in season 2.
God and Satan are major characters in this series.One is the Man, and the other is Doris. But which is which?
For fulfilling his task, The Man will be killed.He'll be accused of kidnapping and arrested/killed. It'll, of course, help him "feel what they feel."
The Man is Prometheus hiding from the Gods and Titans as he's escaped from his punishment.Prometheus was the Titan of Foresight who brought fire to Man so that they grow.
The Man is The Doctor.And the booth is the TARDIS.
The Man is The Master.The Doctor has trapped him in the booth, and ordered him to help people, but the Master is using the "tasks" to hurt people instead of just helping them.