Metallica is made up of the four members I've mentioned above, Jason being the replacement for Cliff Burton, who was Metallica's bassist. Here is a little about each member:

Kirk Hammett: Lead guitarist.

Jason Newsted: Bass guitar.

James Hetfield: Vocals and guitar.

Lars Ulrich: Percussion.

For the history of Metallica HISTORY

Here is a picture in memory of Metallica's bassist Cliff Burton, who's work will not be forgotten