He's one of the biggest subjects of the "What could have been" conversation. Not only did Kurt Cobain define an era of music; his music changed the industry. Forever.

It's a feeling of getting old, knowing Kurt Cobain would have been 45 today. But, it's the not knowing that's painful. Not knowing what Cobain and Nirvana could have done had he made a different choice that fateful April 8, 1994.

But, we can salute Kurt today on his 45th birthday. A man who changed rock music can easily be celebrated despite his tragic circumstances.

From Nevermind to In Utero, he sold more than 50 million albums worldwide, played some rockin' tunes and wrote lyrics that has changed lives. Happy birthday, Kurt.

Nirvana: Smells Like Teen Spirit
Nirvana: Heart Shaped Box
Kurt Cobain: 1993 Interview with MTV