If ever there was a constant figure in rock 'n' roll — sideman, bandleader, or otherwise — it's Nils Lofgren. From time fronting his own band, Grin (which lasted 1971 to 1974), to his tenure in Bruce Springsteen's E Street Band, it's as if Lofgren and his guitar have always been there. And for close to 50 years, they have.

Lofgren is celebrating the release of "UK2015: Face the Music Tour," an extraordinary live rendering of his duo work with multi-instrumentalist Greg Varlotta. The album came together upon the urging of Lofgren's wife, who heard live album potential night after night during the duo's latest UK tour.

Lofgren is now back storming the highway with The Boss in the E Street Band. When that excursion draws to a close, it'll be back onto the solo train or whatever may scratch the man's itch at the time.

Lofgren answered the phone to answer a few questions about swapping out the accordion for a guitar, playing with Bart Simpson, and being more than simply a sideman. An edited transcript of that conversation follows.

City: So recording these shows for this new live album was kind of last minute?

Nils Lofgren: I was doing a show last February in the UK. I've been going there since 1973 when I was on Neil Young's "Tonight's the Night Tour," and on my own after that. And I was there with Greg Varlotta, who I've played with for 10 years, and it really was my wife, Amy — who has seen me for 20 years — who thought they were the best shows she'd ever seen me do.

Did you hear the potential right off?

I really wasn't aware of that or had an overview like that, and she implored us to record the last half of the tour for a possible live album. So we got a tape recorder in and we ran it each night for the last seven or eight shows. I was surprised when we got home: there was a great album there. The album runs like the show. It's very authentic to what the show is. It's a really nice snapshot of what I've been doing lately with Greg in my acoustic duo format.

After a 26-month tour with The E Street Band, I came back to my own music, and there's just an excitement and freshness when you don't always do just one thing — I came back re-charged. First of all it was like how do you be a bandleader? It seems foreign for a while but it's something I've done probably 70 percent of my 48 years on the road — I've been a band leader — so I've got a lot of experience and miles logged in. But more than the technical playing, it was just the joy and gratitude in the shows that, maybe Amy noticed, that set them apart from my past shows.

You have quite a following in the UK.

The British music scene is how I fell in love with rock 'n' roll. I was a classical accordion player and it was The Beatles and The Stones that got me off the accordion and into rock 'n' roll. And through them I discovered all of it: Stax, Volt, Motown, Muddy Waters, Howlin' Wolf, Little Richard, all of that. So I owe them a debt of thanks and gratitude. And having people show up in these little towns all over after 40-plus years is a beautiful thing.

A lot of people view you as a sideman. Is that accurate?

I'm very proud of the work I've done in a lot of bands: Neil Young, Ringo Starr, Bruce Springsteen and The E Street Band, Willie Nelson, Jerry Lee Lewis, Branford Marsalis, Cab Calloway. I've always been in bands. I don't really feel like a sideman.

You know, you have an instrument, it's loud — there's a powerful opportunity there to contribute something that makes the picture whole and allows you to touch an audience with music. And that's a very sacred gift. I made an album years ago called "Sacred Weapon." I was given a gift I didn't ask for: to hear notes a certain way that led to a career. So sideman doesn't ring true to me because that kinda indicates what you're doing isn't valuable or important, and nothing could be further from the truth when I'm in someone else's band. Of course, when I'm playing with Neil Young or Bruce Springsteen, everyone's staring at them and that's understandable. But not for a second do I confuse that with a lack of importance.

Talk about your own sideman, Greg Varlotta.

I needed someone to play keyboards and guitar and sing well. Not only did Greg do that, but he is an excellent trumpet player, trombone player, and tap dancer. I know it sounds weird but it works if you don't overdo it. And we came up with a very powerful, colorful show, which I like to call heavy metal melodic acoustic. You want to move a lot of the low end. If you tap your guitar, you want it to be like a kick drum, not something thin. Greg and I have hit it off for 10 years and the shows keep getting better.

Are there any current trends in music that excite you?

I don't know, man; I don't really follow trends. I'm just excited by great singing, playing, and dancing. I went to see Macy Gray and she came out and just killed it, one of the best things I've seen in years. I'm still waiting to see Bruno Mars; he's someone new I think the world of. As far as trends: there's so much good and bad music out there, you've just got to keep your ears and heart open.

What's Nils Lofgren's legacy?

I'm the only guitar player in history who has played with both Bart Simpson and Cab Calloway.