A hypergiant (luminosity class 0 or Ia⁺) are the most massive, bright and rare stars in the Universe. They are hundreds of times more massive than the Sun and millions of times brighter, but only live a couple million years before a catastrophic explosion.

Types of Hypergiants

• Yellow hypergiants - rare, unstable, every couple decades they shed their envelope. They might turn into Blue hypergiants before blowing up. Examples of Yellow hypergiants are IRC+10420 and Rho Cassiopeiae
• Blue hypergiants are very hot and bright. they also lose mass very fast due to stellar winds (Every 1000 years they lose 1 solar mass). Examples: Eta Carinae, Pistol Star
• Red hypergiants are the largest but relatively cold. They often pulsate and are surrounded by dust shells. Examples include all of those largest stars you know: Stephenson 2-18, UY Scuti, VY Canis Majoris, Betelgeuse, Antares...

What happens when they die?

• An insane explosion (supernova or even a hypernova)
• Turn into a black hole if its core is more than 20 solar masses (or into a neutron star if its less than that)