Yes they even opened the door for the punk movement to arise, but for bands as Rainbow and AC/DC, I feel their inspiration comes more from the kinks and the Who than for the Beatles. I personally am against any kind of idolatry for any band or musician. Nothing in music happens out of a context, and there are a lot of social, cultural and business factors that also helped their success.

Without saying that at the beginning the Beatles just copied all the american music that came to Liverpool. They actually become artists (in the sense of looking for new things and create) right after their sudden success in the USA.

For the first metal song, which one would it be? And under which criteria?