For the love of Mike/Pete

A minced oath, which in its full form would be, for the love of St Michael or St Peter although some sources dispute this and say that Mike or Pete are simply random names instead of for the love of God. This particular minced oath dates from the late 19th century and the protagonists for St Michael claim that it was a mild soldiers’ oath, St Michael being the patron saint of soldiers. See also For Pete’s sake.