When Sir William Herschel observed Mu Cephei in 1783 he described it as a most beautiful object of a very fine deep garnet colour, that's exceptionally striking when compared to nearby white stars.
In fact, Mu Cephei is an extremely luminous red supergiant and one of the reddest known stars of all. It may be the largest star visible to the naked eye with an estimated radius of 1.15 billion kilometres (710 million miles) or 1,650 times that of the Sun.
In astronomical terms, Mu Cephei doesn't have long to live. It has almost certainly stopped internal hydrogen fusion, and is likely fusing helium into carbon. Whatever the current state, the Garnet star will almost certainly go bang sometime in the "near" future and destroy itself in a massive supernova explosion.