In the phrases, "For the love of Mike" and "For Pete's sake"who is/was Mike and Pete?

For the love of Mike - (euphemistic) for the love of God

https://en.wiktionary.org/wiki/for_the_love_of_Mik...

For the love of Mike. This is a "minced oath" (a substitute for "for the love of God")that refers to "Mike," meaning an Irishman, aka Mick. Variations: "Holy Mike" and "mother of Mike." "Random House Historical Dictionary of American Slang, Volume 1, H-O" by J.E. Lighter, Random House, New York, 1994.

http://www.phrases.org.uk/bulletin_board/5/message...

"Mike" is pre marital" when he can do no wrong, "Pete" is the same guy post marital when he does nothing right. Then after ten years we gain a religious notoriety.

They are euphemisms for "God" or "Jesus" or "Christ." They might refer to the archangel Michael and to St. Peter, or they may just be random names.

A euphemistic variant of for Christ's sake, for God's sake; "Pete" perhaps invoking Saint Peter and Mike, St Michael or perhaps influenced by for pity's sake. Used instead of from Christ's sake as this was seen as blasphemous by early Christians. Also Good grief and similar.

Mike = Saint Michael.

Pete = Saint Peter.