doesn't matter what sub genre just post your favorite metal bands, why you got into them and when.
Pantera - The first true metal band I listened to in 2003. Before I listened to any metal I was pretty much a 3 doors down, nirvana, etc. type of guy. Then one day my friend linked me a song called Cowboys From Hell and the rest is history.
Machine Head - Just got into them a couple years ago but man are they awesome. I didn't even know they started back in 1994.
Chimaira - one of the great modern metal bands, loved these guys since I first listened to them back in 2003.
Gojira - Awesome Death Metal band from France, if you are into Death metal check them out. Just got into them last year
I have more but those are my top bands.