What is the brightest star in the constellation Orion?

Rigel, usually - which surprises people who expect Betelgeuse, and the two do trade places, because Betelgeuse is variable and occasionally brightens past it. Rigel is a blue supergiant around 860 light years away and something like 100,000 times more luminous than the Sun.

Betelgeuse is the interesting one. It is a red supergiant so large that if placed at the Sun's position it would swallow the orbit of Mars, it is nearing the end of its life, and it will go supernova - possibly tomorrow, possibly in a hundred thousand years. It dimmed dramatically in 2019 and 2020, which produced widespread speculation that it was about to explode; it turned out to have ejected a cloud of dust that cooled and obscured part of its surface.

When it does go it will be bright enough to see in daylight and cast shadows at night for weeks, and it is far enough away to be spectacular rather than dangerous. There is also a decent chance it has already happened - it is 500-odd light years away, so if it exploded during the Tudor period the light has not arrived yet, and everyone would find out at once.