VY Canis Majoris is the largest known star in the universe so far. It is a red Hypergiant, making it a somewhat cool star, but it is very close to it's death, only some 500,000 years from now. Instead of making a Supernova, it will explode into a Hypernova, and will also be visable from Earth when it explodes.
The Sun is very tiny compared to VY CMa. Now, think about it this way, you, are sitting at a computer desk, or on your mobile phone/iPod, reading this. You are literally the size of a quark compared to this star. It is hard to wrap your mind around such things.