Abstract We identify the progenitor star of SN 2023ixf in Messier 101 using Keck/NIRC2 adaptive optics imaging and pre-explosion HST/ACS images. The supernova, localized with diffraction spikes and high-precision astrometry, unambiguously coincides with a progenitor candidate of mF814W = 24.87 ± 0.05 (AB). Given its reported infrared excess and semi-regular variability, we fit a time-dependent spectral energy distribution (SED) model of a dusty red supergiant (RSG) to a combined dataset of HST optical, ground-based near-infrared, and Spitzer/IRAC [3.6], [4.5] photometry. The progenitor resembles a RSG of Teff = 3488 ± 39 K and log (L/L⊙) = 5.15 ± 0.02, with a 0.13 ± 0.01 dex (31.1 ± 1.7 per cent) luminosity variation at a period of P = 1144.7 ± 4.8 days, obscured by a dusty envelope of τ = 2.92 ± 0.02 at 1 μm in optical depth (or AV = 8.43 ± 0.11 mag). The signatures match a post-main sequence star of $18.2_{-0.6}^{+1.3}\, \mathrm{M}_\odot$ in Zero-Age Main Sequence mass, among the most massive SN II progenitor, with a pulsation-enhanced mass-loss rate of $\dot{M}=(4.32\pm 0.26)\times 10^{-4} \, \mathrm{M}_\odot \, \text{yr}^{-1}$. The dense and confined circumstellar material is ejected during the last episode of radial pulsation before the explosion. Notably, we find strong evidence for variations of τ or Teff along with luminosity, a necessary assumption to reproduce the wavelength-dependent variability, which implies periodic dust sublimation and condensation. Given the observed SED, partial dust obscuration remains possible, but any unobstructed binary companion over 5.6 M⊙ can be ruled out.