Good question! Our sun is very, very hot, but it is not the hottest star in the universe. The sun, like all other stars, has different stages in its “life”. The physical conditions of the star (including temperature) and its nuclear reactions are different in the different stages. Right now the sun is in the main sequence stage, during which it is about 10 million degrees Celsius (Dickin, 2005). Later in its life, a star may turn into a red giant. A red giant is not very hot at its surface, but its core may reach 1 billion degrees Celsius (that’s 100 times hotter than the sun) (Dickin, 2005). The sun has not reached its red giant stage yet (and probably won’t for another several billion years), but many other stars in the universe are hot red giants.

Not all stars in the universe are the same size. Some stars are much more massive than the sun. The stars which are several times bigger than our sun may turn into supernovae. Supernovae are stars that contract so much that they eventually explode. They may reach temperatures of 3 billion degrees Celsius (that’s 300 times hotter than the sun) right before they explode (Dickin, 2005).

reference
Dickin, A.P. (2005). Radiogenic Isotope Geology: 2nd edition. New York: Cambridge University Press.

NO. The hottest stars have surface temperatures of 50,000 Kelvin degrees. The Sun surface is only 5800 Kelvin degrees, which means that there are hotter starts than the Sun.

The sun is an "averagely hot" star in the universe. There are many stars that are hotter than the sun -- for instance, stars that burn blue are hotter than our sun!

No; in fact, the Sun is a fairly faint, cool star. We don't know exactly what the hottest star in the universe is, but a class of stars called Wolf-Reyet stars (named after the guys who discovered/described them) are currently the hottest/brightest stars known.

No, the Sun is not the hottest star; there are many stars much hotter than the Sun! You can tell the approximate temperature of a star by looking at its color. The coolest stars are red, then orange, then yellow (like our Sun). Even hotter stars are white and then the hottest stars are blue!

The surface temperature of our sun is 5777 Kelvins (~5000 degrees C or ~ 9940 degrees F). The surfaces of the hottest starts can be 10 times hotter than the sun! The center of stars is even hotter than their surfaces.

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No, the Sun is not the hottest star in the universe. In fact, it's not very hot at all compared to the population of stars in the Milky Way galaxy. One way astronomers measure the temperature of stars is by analyzing the light that comes from them: hotter stars burn at blue-UV wavelengths, while cooler stars burn at yellow-red wavelengths. Our star (the Sun) burns at ~5500 C, and is approximately 'white'. When you look at stars in the night sky, you can guess their temperature based on their color. Any star that looks blue is burning much hotter than a red star.