A red supergiant star is a larger and brighter type of red giant star. Red supergiants are often variable stars and are between 200 to 2,200 times bigger than the Sun. An example of a red supergiant star is Antares. 119 Tauri, Betelgeuse, Mu Cephei, Stephenson 2-18 and VV Cephei are other famous examples of red supergiants. Most red supergiant stars explode as supernovae, but some of the brightest become Wolf-Rayet stars before exploding. They are stars that have a  LOT of light. They are the largest stars in the universe If measured in Volume, granting they are not the biggest or Brightest. Betelgeuse and Antares are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars. They are commonly a hundred to a thousand times the sun, but still size is not the only impressing aspect of a Red Supergiant. They are surprisingly cool. Not only that, but they are cooler than the sun.