Metallica guitarist Kirk Hammett is responsible for quite a few guitar solos throughout the band's career. In a recent interview with Metal Hammer, Hammett name his three favorite solos he's ever played.
Hammett names "Hero of the Day", "One", and "Fade to Black" as his favorite three, and reveals the solo from "One" was pretty much written on the spot.
"Lars called me and said, 'Can you come down? We need a solo on the new song demo,'" said Hammett. "I remember showing up with my guitar, Lars played me the track a couple of times and I fiddled with it, figured out where James was going. I said, 'OK, press record.' Next thing I know, my hand is tapping on the neck, following the chord progression, it just came out of air! Afterwards I was thinking, 'Well, that was kind of a trip!'"
Check out all three of Hammett's explanations here.