ABSTRACT We identify the first quiescent galaxies in TNG300, largest volume of IllustrisTNG cosmological simulation suite, and explore their quenching processes time evolution to z = 0. find that with stellar masses M* > 3 × 1010 M⊙ specific star formation rates sSFR < 10−11 yr−1 emerge at ∼ 4.2 TNG300. Suppression these begins a thermal mode active galactic nucleus feedback 6, ki...