I never heard of R-136
R136a1 is more powerful than VY Canis Majoris. R136a1 is a massive and bright star in the R136 star cluster in the Tarantula Nebula, while VY Canis Majoris is a red hypergiant star in the constellation Canis Major. R136a1 is one of the most massive and luminous stars known, outshining VY Canis Majoris.
From Earth the Sun is obviously the brightest star. Otherwise Sirius (The Dog Star) is brightest star discovered so far with a magnitude of -1.42. One of the most luminous stars in the Galaxy is called The Pistol Star (but dust hides it from view) Yes, from Earth the Sun is the brightest star. But that's not the question: the brightest star in the universe is certainly not the Sun, nor is it Sirius; Spica for instance, is over 10 times the mass of the Sun, thus having a far greater luminosity. But the light years separating Spica from Earth reduces it to the 15th brightest star in the nighttime sky. And the Pistol Star is only one of the brightest stars in the Milky Way Galaxy... The universe however, houses many stars superior to the Pistol Star. The problem with the question is it refers to such an astronomical entity, the vast universe. And as such, it may never be able to be answered with complete accuracy... That isn't the question either, the brightest star known in the universe is R136a1, a blue hyper-giant which is not only the most massive star known, at 265 solar masses, but the brightest. It shines at 8,700,000 times the luminosity of the sun and is a member of the R136, a super star cluster around the centre of the tarantula nebula in the the magellanic cloud, a satellite galaxy of the Milky way.
Examples of main sequence stars include our sun (a G-type star), Sirius (an A-type star), and Alpha Centauri A (a G-type star). These stars are in the main phase of their lifecycle, where they are fusing hydrogen into helium in their cores.