  The missing historical record of the Cassiopeia A (Cas A) supernova (SN)
event implies a large extinction to the SN, possibly greater than the
interstellar extinction to the current SN remnant. Here we investigate the
possibility that the guest star that appeared near Cas A in 1592--1593 in
Korean history books could have been an `impostor' of the Cas A SN, i.e., a
luminous transient that appeared to be a SN but did not destroy the progenitor
star, with strong mass loss to have provided extra circumstellar extinction. We
first review the Korean records and show that a spatial coincidence between the
guest star and Cas A cannot be ruled out, as opposed to previous studies. Based
on modern astrophysical findings on core-collapse SN, we argue that Cas A could
have had an impostor and derive its anticipated properties. It turned out that
the Cas A SN impostor must have been bright ($M_V =-14.7 \pm 2.2$ mag) and an
amount of dust with visual extinction of $\ge 2.8\pm 2.2 $ mag should have
formed in the ejected envelope and/or in a strong wind afterwards. The mass
loss needs to have been spherically asymmetric in order to see the light echo
from the SN event but not the one from the impostor event.
