Pulling back the curtain on WWE icon The Undertaker

The Undertaker debuted in late 1990s and continues to be one of the most enduring characters in WWE history. Amer Hilabi/AFP via Getty Images

There's something jarring about hearing The Undertaker chuckle.

Granted, he's not The Undertaker as we speak on the phone, although, in truth, he's always The Undertaker. On the other end of the line is Mark Calaway, the 55-year-old Houston native whose 30-year run with the WWE as "The Dead Man" is unequaled in its longevity and legacy.

It was also unequaled in its secrecy. Calaway has long been notorious for keeping "kayfabe," and not allowing fans to get a glimpse at the man behind the gimmick. That wall has started to crumble in his later years, and it gets demolished in "Undertaker: The Last Ride," a five-episode documentary series on WWE Network that premieres this Sunday.

"I think there's a lot of people that have wanted to see a lot of what they're going to get to see. They just had to wait 30 years for it," he told ESPN on Wednesday, with that aforementioned chuckle.

"But I think people are going to be shocked and amazed, and have a better understanding of who The Undertaker is and who Mark Calaway is."

In a rare interview, we spoke with Calaway about his decision to get candid, the enduring legacy of The Undertaker and whether his "cinematic" WrestleMania match with AJ Styles could add a few more years to his career before 'Taker rests in peace.

ESPN: Like Chris Jericho said in the first episode of "Undertaker: The Last Ride": You don't do podcasts. You don't do interviews. You're not just dropping the gimmick here. You're also allowing people to see you really vulnerable, like the scene where Vince McMahon is running to get help because that's how badly you were concussed after a match. How difficult was it to open yourself up like this?

Calaway: "It was pretty difficult, honestly. But it was my idea. The end is near. [Laughs] I knew that I needed to document some of this stuff, because I wouldn't have another chance to do it. Because once I finally pull the plug, I won't have the opportunity to have footage of me behind the scenes and what I was thinking at the time. I really didn't know what we were going to do with all of this. We didn't start out with any thoughts. We just started filming this stuff with the thought that somewhere down the line we'd maybe do something with it.

"But it was extremely difficult. Even though it was my idea to have a crew start following me, it was extremely difficult for me to get used to it, to let my guard down. They would be there. They'd be filming. And then next thing you know, I'd snap at them, 'Why are you filming me?!' And they'd be like, 'Because that's what you asked us to do.' And I was like, 'Aw, s--- you're right.'

"I'm a notorious old-school guy. When I hear people talking about matches and this and that, I just cringe, because I've always protected the business. Obviously I realize that it's the natural progression and that things have changed. I've changed with it, but there's that certain aspect of it being not for everybody.

"That's one reason why The Undertaker had the longevity that it did. Because all they got was The Undertaker."

Now you're like a magician who decided to start explaining the tricks.

Calaway: "Exactly! So it was really difficult at first to let the guard down. [For example], it took me forever to get on the social media thing. A couple of years ago, I started a social media account, and I started getting things like 'The Undertaker is on Instagram. My childhood has been ruined.' [Laughs] That's how protective I was of that character. So some people are really receptive to the fact that I'm opening up. Others are acting like I've ruined their childhood."

Wrestling has seen its share of gimmicks through the years that are over the top, but they always seem to have a shelf life. Fans grow tired of them as times change. Ric Flair said that "The Undertaker" is the best gimmick in wrestling history, and it's one that has lasted for decades. But was there ever a time when you were worried about The Undertaker character having run its course? That things maybe were pushed too far?

Calaway: "You run that risk. Especially when you have up to six hours of content a week on television. Regardless of the character, any talent runs the risk of burning themselves out, based on that content alone. And then as all the -- this is the only way I know how to say it -- but all the 'smart marks' and all the dirt [sheets] became such an obsession, it was hard for characters to stay viable. You become a flavor of the week.

"I think what really helped me [stay viable] was that I did protect that character. I didn't give them anything other than the character. You didn't see me doing movies as something else. I had opportunities to do that other stuff, but I passed. I knew wrestling. I knew WWE. I knew Vince. That was my passion, and to this day [it still is]. I knew I couldn't be [The Undertaker] here, and then go do something else. I don't think people would have accepted it and stayed intrigued in the character.

"When I started feeling stale in the Attitude Era, I thought that if I didn't change the character, I don't think it would have lasted through that era. It was everything goes, reality based. That's when I switched to the American Badass character. I kept some elements of The Undertaker. Kept the name. But I took the shackles off for a little while for how that character presented itself. And it worked. People accepted it, and it fit for that time period. Once I felt like it ran its course, I was able to bring [the Undertaker] right back. Now I had elements of the original Undertaker, elements of the American Badass and I was able to keep adding to the character while staying true to it. That's what's given it the longevity that it's had: Adapt, but keep the core elements of it."

One of the previews for the series shows you watching the Roman Reigns match from WrestleMania 33 and being "so disappointed in your performance."

Calaway: "That was one of those times it was tough having the cameras there. That was the first time that I watched that match back. I was so disgusted with it that I didn't want to watch it back."

For someone who took so much pride in his in-ring performance, what was it like when you revisited matches that didn't work? Is that something you found constructive?

Calaway: "So, a little insight into how we used to do things.

"We used to have a pay-per-view on Sunday, and then obviously do TV on Monday. During catering, they'd be replaying the pay-per-view from the night before. Everybody would be watching the matches. I couldn't do it. I cannot watch myself in that atmosphere. I wouldn't watch my matches back until I was by myself, at home. No wife, no kids, nothing. I had to be by myself, alone. I wasn't looking for the good stuff. I was looking for the bad stuff. What I should have done when I did that [move]. I wanted to pick it apart. You can watch a match with your peers and they'll be like, "Aw, man, that was awesome." I don't want to hear that.

"Early on in my career, I watched everything back. Good, bad, indifferent. As I got older ... I know when I'm out there and I'm moving slow. I know when my limp is more prominent that it may be. Or when I'm behind in a spot. I just know now.

"[Watching that match], I'm battling with it. I was so disappointed for Roman. Even after Brock Lesnar beat the streak, for guys coming up to have a match against The Undertaker at WrestleMania -- especially where Roman was at -- it was important for his career. Especially because he was going over. For me, in that role, I wanted to do the very best that I could do for Roman. I think the world of him. You want to be able to do the best you can for him, and you know you have no business being in the ring.

"Yes, I could have mailed it in. Protected myself. Only done a couple of things that I knew that I could do. But that's just not the way I work. And it wouldn't have been fair to him. So I just tried to do the best I could. The harder I tried, the more I did -- at least in my perception -- it was not a good night. It was really disappointing. Watching it back finally, and watching it back in front of a film crew, it was like ... I didn't have to say much. You could just tell from the expression on my face that I wasn't really pleased with it."

Undertaker, AJ Styles throw down in epic 'Boneyard' match

Undertaker and AJ Styles square off in the 'Boneyard' match at Wrestlemania 36.

Let's talk about a match people were pleased with. The Boneyard match with AJ Styles at WrestleMania 36 went over big with fans. Were you surprised by that reaction, and does the "cinematic" match thing extend your career beyond what your expectations might have been?

Calaway: "I think it could, if I wanted to do that. That possibility is there, but we'll just see on that.

"We were both very proud of that match. Considering all the circumstances, we were really, really happy with it. And the fact that we got to go offsite and give it a theme like that, it helped tremendously. Like I've said, for me, it's always, always about the story. I tell this to people all the time: Wrestling isn't about the moves. It's about telling the story. You use wrestling moves to tell that story, but that's not what it's all about. He went places in his promos leading up to WrestleMania that no one has ever dared go, you know? After all those interviews, even if we had had a regular match ... you talk about my wife, and it would have been all fists anyway.

"I'm not trying to armdrag and armbar and do all that stuff. I'm going to punch you in the face until your nose meets the back of your head. Because that's real, you know what I mean? Because of the intensity of his promos, and then going to [the boneyard], I think we really told a great story. At the end of the day, that's the most important part.

"The way it was shot, I mean my goodness, it was a mini-movie. I just really think it's going to catch on. Bray Wyatt's character is probably the closest to mine. He's got that really over-the-top demented type character. He could do some things in that realm that would be just phenomenal. We were the trendsetters there. I think there will be more cinematic matches like that in the future.

"As for me ... we'll see what happens with me. But I was really happy how that came off."

Well, we know to never say never when it comes to the Undertaker returning.

Calaway: "Never say never."