Some thoughts upon the delicate subject of Theodicy. Or something like that.

Satan is a function of God. In Job, ha-satan, 'the adversary' is a member of the Lord's divine council and plays, well... devil's advocate
It's only in the New Testament and some apocrypha, that satan becomes a Satan in the proper, and turns into a more duelistic figure. Some scholars have suggested it might be due to Jewish contact to Zoroastrianism during the Achaemenid Empire's overrule. Asking God to deliver oneself from temptation makes sense, when one remembers scenes of God testing people through the Scriptures, effectively 'tempting' them on several occasions; tempting choices that tend to lead to 'evil' results.

As for the originality of the Lord's Prayer - it's ideas are expressed all throughout the Hebrew Bible, but it's only recorded as we know it through the lips of Jesus, making it a Christian prayer, pretty much.