The brightest star visible from Earth is the sun. Though it is not exceptionally bright by the standards of other stars, its relative proximity to Earth makes it, by far, the brightest object in the sky, with an apparent magnitude of -26.74.
The brightest star in the nighttime sky is Sirius. Sirius has an apparent magnitude of -1.46 and is visible from a distance of 8.6 light years.
The brightest star ever discovered, excluding supernovas that can temporarily outshine the galaxy they are in, is designated R136a1, according to The Independent. This star is located inside the Large Magellanic Cloud. It weighs 300 solar masses and shines nearly 10 million times brighter than the sun.