Cepheus's own article rightly centres Delta Cephei, the variable star that gave its name to an entire class of distance-measuring stars. A different star in the same king's figure earned its own name for the opposite reason: not for blinking on a schedule, but for its colour.
Mu Cephei is a red supergiant so deeply coloured that William Herschel, cataloguing the sky in the late eighteenth century, nicknamed it the Garnet Star. It is among the largest and most luminous stars known: were it placed at the centre of the solar system in the Sun's position, its outer atmosphere would extend out past the orbit of Jupiter, swallowing every inner planet and several outer ones along the way. Its intense red colour comes from a surface temperature far cooler than the Sun's, cool enough that the star radiates chiefly at wavelengths the eye reads as deep red rather than white or yellow.
Where Delta Cephei matters because its brightness changes on a precise, reliable clock, useful for measuring distance, Mu Cephei matters for almost the opposite reason: it barely needs measuring to be remarkable, since its sheer size and colour are obvious to anyone who points a telescope at it, no instruments or calculation required beyond noticing how red it is.
Two stars in one small constellation, one useful because it is regular, the other startling because it is extreme.