  The X-ray binary 4U 1954+31 has been classified as a Low Mass X-ray Binary
(LMXB) containing a M giant and a neutron star (NS). It has also been included
in the rare class of X-ray symbiotic binaries (SyXB). The Gaia parallax,
infrared colors, spectral type, abundances, and orbital properties of the M
star demonstrate that the cool star in this system is not a low mass giant but
a high mass M supergiant. Thus, 4U 1954+31 is a High Mass X-ray Binary (HMXB)
containing a late-type supergiant. It is the only known binary system of this
type. The mass of the M I is 9$^{+6}_{-2}$ M$_\odot$ giving an age of this
system in the range 12 - 50 Myr with the NS no more than 43 Myr old. The spin
period of the NS is one of the longest known, 5 hours. The existence of M I
plus NS binary systems is in accord with stellar evolution theory, with this
system a more evolved member of the HMXB population.
