  We present evidence in support of the hypothesis that the young stellar
object RNO 54 is a mature-stage FU Ori type source. The star was first
cataloged as a ``red nebulous object" in the 1980s but appears to have
undergone its outburst prior to the 1890s. Present-day optical and
near-infrared spectra are consistent with those of other FU Ori type stars,
both in the details of spectral line presence and shape, and in the overall
change in spectral type from an FGK-type in the optical, to the M-type
presented in the near-infrared. In addition, the spectral energy distribution
of RNO 54 is well-fit by a pure-accretion disk model with parameters: $\dot{M}
= 10^{-3.45\pm0.06}$ $M_\odot$ yr$^{-1}$, $M_* = 0.23\pm0.06 \ M_\odot$, and
$R_\mathrm{inner} = 3.68\pm0.76 \ R_\odot$, though we believe
$R_\mathrm{inner}$ is likely close to its upper range of $4.5 R_\odot$ in order
to produce a $T_\mathrm{max} = 7000$ K that is consistent with the optical to
near-infrared spectra. The resulting $L_\mathrm{acc}$ is $\sim 265 \ L_\odot$.
To find these values, we adopted a source distance $d=1400$ pc and extinction
$A_V=3.9$ mag, along with disk inclination $i=50$ deg based on consideration of
confidence intervals from our initial disk model, and in agreement with
observational constraints. The new appreciation of a well-known source as an FU
Ori type object suggests that other such examples may be lurking in extant
samples.
