  We have constructed a series of non-rotating quasi-hydrostatic evolutionary
models for the M2 Iab supergiant Betelgeuse ($\alpha~Orionis$). Our models are
constrained by multiple observed values for the temperature, luminosity,
surface composition and mass loss for this star, along with the parallax
distance and high resolution imagery that determines its radius. We have then
applied our best-fit models to analyze the observed variations in surface
luminosity and the size of detected surface bright spots as the result of
up-flowing convective material from regions of high temperature in the surface
convective zone. We also attempt to explain the intermittently observed
periodic variability in a simple radial linear adiabatic pulsation model. Based
upon the best fit to all observed data, we suggest a best progenitor mass
estimate of $ 20 ^{+5}_{-3} M_\odot$ and a current age from the start of the
zero-age main sequence of $8.0 - 8.5$ Myr based upon the observed ejected mass
while on the giant branch.
