Question: Who is Pete in the phrase "For Pete's Sake?"? 

Answer: Here is an explanation from The Phrase Finder supporting the Saint Peter hypothesis:\n\n: : What is the origin/menaing For Pete's Sake?\n\n: Biblical origins. Think of St Peter. Think of the omnipresent medieval church and think of hitting your thumb with a hammer. You can't swear, else the local priests will have you up before the Bishop and the Lord alone knows what the outcome of that will be, so you exclaim, in appropriate tone of voice, "For Saint Peter's sake" and carry on erecting the shelves. This phrase was amended to "For Pete's Sake" in later, less religiously oppressive, times.\n\n: This is called a "minced oath," a substitution of a less offensive word.
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