Bob Dylan
Frank Sinatra
Black Sabbath
Led zeppelin, who sold the 2nd most albums of all time
I don't think they were metal; to me they sound more like heavy blues rock. But aside from that, Black Sabbath formed earlier, and in contrast, were and are definitely metal. In fact, Judas Priest (whom no-one bar Gerard Way will say are not a metal band) formed the same year as Zeppelin.
Black Sabbath
Black Sabbath
AC/DC sold more records than Black Sabbath, but Sabbath came before AC/DC, have a larger body of work, and are more versatile musicians.
Iron Maiden
The Rolling Stones
Bob Dylan
Frank Sinatra
Led Zeppelin
Lp all the way baby
Black Sabbath
Black Sabbath
In general, Led Zeppelin is more popular than U2. Yes, U2 has been probably the biggest band in the world since the 1980s; but Zeppelin still sold more records than U2 did, so Zeppelin's the answer.