Wiktionary
of all
adv. 1 (non-gloss definition: Used as an intensifier with superlative forms of adjectives). 2 (non-gloss definition: Used as an intensifier with nouns to denote being ultimate.)
Usage examples of "of all".
There must be lots of other places they can go, out of all them bright stars up there behind the clouds.
He became renowned as a man pursuing a dream, though no one knew its nature-least of all the Wanderer himself.
There was much smiling and laughter, then saying of farewells, last of all a farewell to his sons, whom he had left behind Occupants of a different land, another life.