What four legendary rockers made up the "Million Dollar Quartet"?

The Million Dollar Quartet album:

As everyone knows, it's not really a quartet because Johnny Cash wasn't caught on tape. But Elvis, Carl Perkins and Jerry Lee Lewis were --and this was the first time Elvis met Jerry Lee, who was at the time just the pianist on Carl's session. At this point in time, Elvis was already recording for RCA -- so it was quite a treat to have him drop by the Sun Studios.

One of the highlights of the tape is Elvis telling the others about seeing one of Wards Dominoes (in fact it was Jackie Wilson) imitating him in Las Vegas. Elvis then imitates Jackie Wilson imitating him! Elvis also sings a version of Paralized (a song he had already recorded) in the style of Wilson -- and it is much better than the real recording!

Thanks!