  We analyze pre-explosion near- and mid-infrared (IR) imaging of the site of
SN 2023ixf in the nearby spiral galaxy M101 and characterize the candidate
progenitor star. The star displays compelling evidence of variability with a
possible period of $\approx$1000 days and an amplitude of $\Delta m \approx
0.6$ mag in extensive monitoring with the Spitzer Space Telescope since 2004,
likely indicative of radial pulsations. Variability consistent with this period
is also seen in the near-IR $J$ and $K_{s}$ bands between 2010 and 2023, up to
just 10 days before the explosion. Beyond the periodic variability, we do not
find evidence for any IR-bright pre-supernova outbursts in this time period.
The IR brightness ($M_{K_s} = -10.7$ mag) and color ($J-K_{s} = 1.6$ mag) of
the star suggest a luminous and dusty red supergiant. Modeling of the
phase-averaged spectral energy distribution (SED) yields constraints on the
stellar temperature ($T_{\mathrm{eff}} = 3500_{-1400}^{+800}$ K) and luminosity
($\log L/L_{\odot} = 5.1\pm0.2$). This places the candidate among the most
luminous Type II supernova progenitors with direct imaging constraints, with
the caveat that many of these rely only on optical measurements. Comparison
with stellar evolution models gives an initial mass of $M_{\mathrm{init}} =
17\pm4 M_{\odot}$. We estimate the pre-supernova mass-loss rate of the star
between 3 and 19 yr before explosion from the SED modeling at $\dot M \approx
3\times10^{-5}$ to $3\times10^{-4} M_{\odot}$ yr$^{-1}$ for an assumed wind
velocity of $v_w = 10$ km s$^{-1}$, perhaps pointing to enhanced mass loss in a
pulsation-driven wind.
