By just about anyone's estimation, Rey Mysterio has already had a career worthy of the Hall of Fame.

The legendary luchador has showcased his transcendent brand of wrestling across the biggest promotions in the world since he debuted as a 21-year-old for WCW in 1996. Mysterio revolutionized the business from an in-ring standpoint in his five years with the company, even if he never reached the heights someone with his talent deserved. He got the chance to do that when he debuted with WWE in 2002 and blossomed into a mainstream star during his nearly 13-year run.

Mysterio could've easily called it a career when that run came to an end in 2015, and no one would've thought otherwise. His in-ring innovation and collection of matches have already more than stood the test of time. But now, almost three years after his WWE exit, Mysterio still isn't done adding to his legacy. At 43 years young, he's one of the hottest free agents on the market.

"I'm not locked up to any company. I'm an independent contractor, as we say," Mysterio said in an interview with ESPN.com. "I could go work wherever I want. That's the beautiful thing about being on this side of the fence. You don't have a commitment with only one company. You can go around and pretty much wrestle wherever you want. You can choose when you want your off-days to be. That was one of my main priorities when I left WWE."

Mysterio has spent those two-plus years wrestling across the independent scene and satisfying dream matchups many fans never thought possible.

Mysterio has wrestled AJ Styles, Jeff Hardy and Kurt Angle outside WWE walls. He's also had the chance to face dynamic high-fliers Will Ospreay and Ricochet several times across various promotions. Mysterio has taken full advantage of having control of his dates, something that is increasingly more important given the eight surgeries he's undergone on his left knee.

"I told myself, once I started feeling aching and I was having hard times getting up from my bed in the morning when I woke up, it was gonna start getting close to that time [to quit]. I was feeling that right towards my end of the last year or so of WWE," Mysterio said. "It came to the point where I was feeling like that constantly. I didn't want to fall into another phase of taking either medication to ease my pain. I wanted to use the rest way to heal my body up. Believe it or not, the last two years, I don't think I've felt better."

Mysterio's improved mobility has allowed him to wrestle without a knee brace for the first time in 15 years. He says with the exception of when it's cold or raining outside, he no longer feels pain in his left knee. The now-rejuvenated Mysterio was able to make those dream matchups live up to the hype, but fans were eager to see him on TV again. They finally got the chance when Mysterio signed with Lucha Underground for the show's second season.

Former WWE superstar Rey Mysterio recently appeared in Tommy Dreamer's House of Hardcore. Courtesy of Tommy Dreamer / House of Hardcore

While Mysterio's two-season run with Lucha Underground was successful, including memorable matches against the likes of Prince Puma (Ricochet), Johnny Mundo, Pentagon Dark and Matanza Cueto, the ending to his tenure with the show was head-scratching.

However, Ultima Lucha Tres, Lucha Underground's biggest event of the year split into four parts this season, didn't feature the show's biggest star. Mysterio still isn't sure why he was left off the card after main-eventing Ultima Lucha Dos a year earlier, but he thinks a miscommunication between him and Lucha Underground had something to do with it.

"I wanna say that it might have been a mix-up of dates," Mysterio said. "We were trying to squeeze some dates in that I didn't have contemplated, so that might have been the case because they record the shows and air them later. I'm sure that could've been fit in somewhere along the line to eventually make me part of that Ultima Lucha, but whatever the case was, I wasn't part of it. I think the fans that appreciate my work can recognize the fact that there was something missing there."

Mysterio is open to appearing in Lucha Underground's recently announced fourth season, but there haven't been any negotiations between the two parties. For that reason, speculation has already started for Mysterio's long-awaited return to WWE.

It is Royal Rumble season after all.

Rey Mysterio on 205 Live Mysterio, widely-regarded as the greatest cruiserweight in pro wrestling history, struggles to understand why 205 Live hasn't grown in popularity despite the depth of its roster. "I don't know [why 205 Live isn't more popular]," he says. "To be honest with you I can scratch my head all day and not figure it out because they do have talent. I don't know if they're limited to doing so much in the ring that they don't go all out versus Lucha Underground. It's Johnny Mundo versus Rey Mysterio and 15 minutes. We'll go ahead and tear the house down without limitation. We'll be coming up with new moves and still trying to innovate the game. "With [205 Live] and the comparison with WCW, it was just a different time. Back then, we had no competition. The cruiserweight division had no competition. Nobody was out there doing the stuff we were doing. You have to get really creative now to blow the fans' minds away. I think it's gotten to that point where there's another phase of the evolution of the sport and it's changing right now as we speak. "I see guys like Ricochet. I see guys like Will Ospreay. And I'm going, 'what the hell, where are these guys coming up with all these moves?' Sometimes I pause and think, 'I was like that when I was breaking into the business'. I was always being creative and thinking of new stuff. We're in a new era right now. I think if they just let the guys from [205 Live] go a little bit more, feel free to do whatever they want to do, maybe they might get a different reaction. I could be wrong."

"Never say never, right?" Mysterio said of his chances of entering the 2018 Royal Rumble.

WWE ramped up the buzz even more by including Mysterio in a video listing five superstars fans want to see return in 2018. Mysterio is more than willing to make his WWE return, even if there haven't been any discussions yet.

"I actually did get a chance to see that post, and I was surprised, because the post is one thing, but there hasn't been any communication between either side," Mysterio said. "Again, anything can change. Things happen last minute sometimes, and that's what makes it exciting for the fans. The fact that they don't know ahead of time lets you know they're being surprised."

Mysterio knows the ending of his WWE career wasn't fitting for a star of his magnitude. He last appeared for the company the day after WrestleMania XXX and had to wait nearly a year before his contract expired. Mysterio hopes he can still have a proper send-off with WWE.

"This is the way I was thinking at the time, and I still think that to this day. When I left WWE, from my understanding and from the time that we sat down ... that I decided not to re-sign another contract with WWE was for me to get some off time," Mysterio said. "I never meant or insinuated in any way or form that I was gonna leave for good. I think that should say a lot. I wasn't announcing that was the end of Rey Mysterio's career.

"I would definitely love to go back and finish up. Whether it's one year or whatever the case might be. Whether it's a farewell. I owe a lot to that company. That company gave me such an amazing opportunity, and I took advantage of every single moment I was with WWE to the fullest. I wouldn't want to just be remembered as 'Oh, man, he never re-signed and he never came back.' I would definitely love to come back and do a last run and say goodbye to my WWE fans. Tell them goodbye in a proper way."

Rey Mysterio's high-flying style has made him a superstar in the ring for decades. WWE

While Mysterio hopes a final WWE run is in his future, he also knows at 43, with his history of injuries, he'd have to work on a part-time basis.

"I don't think I can go back [to a full-time schedule]. There's just no way," Mysterio said. "I can't go back to that schedule. It would be common sense for them as well. That was my main motive for stepping away. I wanted to be able to have some free time. I'm still working really hard right now on the independent scene, but I control my schedule. I might get booked three days -- Friday, Saturday, Sunday, come home Monday, and the following weekend I don't have to work. That right there gives me a peaceful state of mind like you have no idea."

In addition to his independent bookings, Mysterio has also shifted his focus to helping jump-start the career of the next great Mysterio -- his son, Dominik.

Dominik has grown considerably since the on-screen battle for his custody between Mysterio and Eddie Guerrero in 2005. He is now 21 and towers over his legendary father. Mysterio has his wife to thank for that.

"That's where the genes come from. From her side, definitely not my side," Mysterio admitted. "Hopefully with those genes and a little bit of my academic genes, hopefully he can do very well. Even succeed from what his dad has done."

Mysterio started training Dominik a year ago, but a nagging lower-back injury forced his son to sit for several months. Dominik felt "sluggish" upon his return to training about two months ago after he picked up extra weight during his time off. That gave Mysterio the idea of sending his son to work for Chris Cavallini of Nutrition Solutions in Tampa, Florida, to get back into shape and limit the distractions of living in San Diego.

Dominik now follows a strict regimen, waking up every day at 6:30 a.m. to start his daily physical therapy training, help pack food and be in bed by 8 p.m. Mysterio is excited to see Dominik's progress in person when he comes home for the holidays, as he hasn't seen his son for about two months.

After New Year's, Dominik will begin fourth months of training at Jay Lethal's school in Tampa.

Mysterio, who was trained by his uncle Rey Misterio Sr. at the age of 14, hopes he's giving his son the best chance to succeed.

"I wanna say that I think I'm doing things the right way, but this is my first time going through this," Mysterio said. "I know how my uncle trained me, and it was very different. It was very old-school. It was very grimy and grinding, so I'm trying to do it in a different way but have him still appreciate the sport."

While Mysterio says "it would be perfect for me to at some point say farewell and leave my son behind and have him take over," he's still not ready to say goodbye. He still enjoys wrestling at independent shows of his choosing, such as his own Lucha Wonderland event on Friday. He knows he has unfinished business with WWE and wants the chance to properly say goodbye to those fans. He says he's also hoping to check a box on his bucket list by getting the chance to perform for New Japan at the Tokyo Dome like his close friend Chris Jericho.

To put it simply, Mysterio is feeling too good and fielding too much interest to stop now.

"I've always said that once I lose that feeling of not being excited before I go into a ring or feel that sensation of the butterflies, jittery-sensation in your stomach, then that's the time I have to step away," Mysterio said. "But I still get that sensation. I still have a lot more to give."