"Mystery Train" (Elvis Presley)

Before the song "Heartbreak Hotel" made him a household name, Elvis Presley had cut several sides for producer Sam Phillips at Sun Records in Memphis between 1954-55.  His final recording for Sun and his first #1 charting single was the country song "I Forgot to Remember to Forget."  
But I want to discuss the flip side of that single: "Mystery Train."
I'll start by saying, as a child of the late 70s, the image of Elvis that was burned into my brain at an early age was the puffy, sweaty Elvis in sequined jumpsuits who struggled to remember lyrics.  You know, the kind of caricature that you'd find some two-bit impersonator with a beer gut and pair of mutton chops trying to pull off at a drive-thru wedding chapel a couple of miles off the Strip.  Even as a kid, I had no time for that kind of Lost Wages kitsch, so I kind of turned my nose up at Presley's whole catalog and career.
It wasn't until I got a bit older and started exploring my dad's record collection that I first heard a couple of Presley's early recordings, and they blew me away.  They were raw and boundless in their fusion of country and R&B.  Not what I'd been conditioned to expect at all.
What surprised me most was that nothing sounded contrived.  
(Slightly derivative?  Maybe.  Insincere?  Not in the least.)
I guess the cynic in me was expecting the music to sound transparently money-grubbing—kind of like when producers in the 2000s started tossing together the hottest rapper of the moment with the hottest pop-country star of the moment on duets that played to the lowest common denominator of both fan bases.  (I'll let you, dear reader, do a Google search for yourself to find examples.)
But what I heard instead was three blue-collar guys from Memphis, jamming on their favorite country tunes in the style of their favorite R&B tunes, and vice versa.  And it not only worked, but it was electrifying.
Which brings me to 1955's "Mystery Train," a straightforward blues tune that was originally written and performed by blues artist Junior Parker for Sun Records in 1953.  Presley, lead guitarist Scotty Moore, and bassist Bill Black take the basic structure of Parker's song and then "countrify" it with that galloping rhythm/riff, which worms its way into your core within the first 3 seconds of the intro.
What I love about this track overall is the recorded-live feel—not to mention that glorious 1950s slap-back reverb on all of the instruments.
But Presley's vocal truly steals the show.  From effortlessly hitting those high notes on Train! Train! down to the low notes that cap every stanza, it's a helluva performance.  The icing on the cake is the little oooh-woo! he lets out at the end, sounding like a train whistle trailing off into the night.  It's obvious he was having the time of his life.

"Jailhouse Rock" (Elvis Presley)

When I think of Elvis, I don't immediately think of "Hound Dog."  Or "Love Me Tender."  Or "Don't Be Cruel."
It's always "Jailhouse Rock" (1957).
The Jerry Leiber-Mike Stoller composition was written for the movie of the same name.  Actually, to be accurate, the film's working title was The Hard Way when the writing duo received the film treatment.  The title only became Jailhouse Rock after Leiber and Stoller penned the song and the studio realized it was going to be the centerpiece of the film.
Story goes, Leiber and Stoller had been flown in from Los Angeles to New York to meet with Atlantic Records owners, Nesuhi and Ahmet Ertegün, about writing and producing for the label.  They'd also been commissioned by the producer of The Hard Way (a.k.a. Jailhouse Rock) to write music for the film.  But instead of spending their time writing music in their hotel room, they were busy hanging out at jazz clubs every night and soaking in the city by day.  
Time passed.  Deadlines, too.
Finally the film's music publisher decided to drop by their hotel, just to see what kind of progress they were making, which was none.  After lecturing them about the importance of meeting deadlines, he pushed a sofa in front of their door and barricaded them in the room until they fulfilled their obligation.
Leiber and Stoller ended up churning out four songs that afternoon, including "Jailhouse Rock," just so they could get the publisher off their backs and hit the town again.  They had no clue the song was going to be a massive hit.
In any case, it's hands down Presley's hardest rocking song.  I'd even venture to say it was the hardest rock song produced up to that point.  From the moment the drums and that clanging, two-chord guitar intro kick in to Scotty Moore's righteously unhinged solo, it burns like a five-alarm fire.
It's also Presley's best (rock) vocal: gritty, full of attitude, and delivered with confidence.  Personally, I hear the echoes of that performance in everything from Van Morrison's vocals for the band Them to Kurt Cobain's scream on the chorus of "Smells Like Teen Spirit."