The popular idiomatic expression the mother of all (something) means:
- an extreme example of something. Donny's car crash was the mother of all crashes. Hundreds will travel to Stonehenge, the mother of all places to celebrate the longest day of the year.
From: Cambridge Dictionary of American Idioms
It appears that it was originated during a famous speech by the president of Iraq in 1991: Etymology:
- Calque from Arabic; popularized in 1991 after its use by Saddam Hussein, then president of Iraq, in reference to the Gulf War as ام المعارك (umm al-ma‘ārik, “mother of battles”).
Ngram shows earlier usages but was the phrase commonly used before 1991, and if not, what alternative idiomatic expression, if any, was used to convey the same concept?