As Billlboard celebrates the first 25 years of the 21st century with charts recapping the top artists, albums and songs in that span, we're also looking back at 25 of the most noteworthy headlines ...

As Billlboard celebrates the first 25 years of the 21st century with charts recapping the top artists, albums and songs in that span, we're also looking back at 25 first-time feats, spotlighting ...