Why did The Undertaker leave WWE in 1999?
 

This was around the time he teamed with Big Show. Then he came back as The American Badass in 2000

It was a combination of time off and some injuries suffered during that time off.

He originally went out with an injury (groin, I think) and then while re-habbing, tore his pectoral muscle.

He lost his smile.

I didn't even know he had one, but there you go.

He never had a smile, he lost his scowl.

The second time (after Survivor Series) he lost it again, but found a hat instead.

You can't do any of that... without a hat.

You crazy guys, that's not the truth.

He had to regenerate. He is dead you know. All good dead people have to regeneraet now and then back in the crypt. He had postponed his for a long time and had been exposed to much daylight. Plus he's normally only seen around winter. When Medusa allows him to prowl the planet.

And the reason he was gone so long is because this time he had to regenerate enough that he could take a wife and sire an heir. Thankfully he accomplished this shortly before he was buried by Kane and Vince McMahon.

I always think they could've have made something off his departure. Instead it looked like he just got bored and wondered off.