of all

/AH1 V AO0 L/
adverb
  1. 1

    Used as an intensifier with superlative forms of adjectives.

    โ€œBest of all was the bicycle I got.ย ย  First of all, I'd like to thank my agent.ย ย  He was the greatest playwright of all.โ€

  2. 2

    Used as an intensifier with nouns to denote being ultimate.

Source: https://en.wiktionary.org/wiki/of%20all