Wladimir Klitschko: Can any of today's rising heavyweights knock off the king?

"Game of Thrones" had The Mad King. Boxing has The Entirely Sane and Pleasant King. That is Wladimir Klitshcko, who has ruled the heavyweight roost since manhandling Chris Byrd way back in 2006 to win the IBF heavyweight title. And now, with Klitschko near his 39th birthday and showing no signs of slowing down his utter domination of the division, it's worth wondering if he's ever going to lose again, or even be seriously tested.

Since that win over Byrd, Klitschko has added the WBO and WBA heavyweight titles to his luggage, and has easily dealt with any challenger in his way, be they opponents thought to be legitimate challengers, or Jean-Marc Mormeck, Alex Leapai, or Mariusz Wach.

The last generation of "rising heavyweight challengers" has had their shot. David Haye, Alexander Povetkin, and Kubrat Pulev were supposedly fighters with the skills and backgrounds -- Haye in the cruiserweight division, Povetkin and Pulev largely in the amateur ranks -- to give Klitschko a run. None of them did.

In 2011, Haye clutched and grabbed en route to a 12 round decision loss he infamously blamed on an injured toe, betraying years of trash talk and boasting in a limp effort that showed him less a lion than a lamb. In 2013, Povetkin made for an ugly night by delivering little on offense, getting dropped four times, and making Wladimir just uncomfortable enough that the champion was holding when he wasn't handily winning. A brave Pulev was wiped out in five rounds last November, showing that if you make Klitschko throw his hands, he's deadlier and just as untouchable at this point.

Right now, there are five unbeaten heavyweights out there, two from the United States, who could potentially be the man to dethrone Klitschko (63-3, 53 KO). Do any of them have a serious chance, or will Wladimir continue trouncing his opposition until the time when he's tired of doing so, and retires from active competition?

Bryant Jennings

Jennings, 30, will get next crack at the champ, as he's scheduled to face Klitschko on April 25 at Madison Square Garden. It's Klitschko's first fight on American soil since 2008, when he handily and boringly defeated Sultan Ibragimov at the same venue. There has been talk of Wladimir coming back to the States the last few years, and now with an American challenger ready, the time is right.

Klitschko has fought three Americans since he last fought in America, beating Tony Thompson twice, plus Hasim Rahman and Eddie Chambers. All of those fights took place in Germany, and all of them were easy night. Jennings (19-0, 10 KO) really came onto the scene in 2012, when he began being regularly featured on NBC Sports Network's Main Events series, scoring five wins that year over Maurice Byarm, former titleholder Siarhei Liakhovich, Steve Collins, Chris Koval, and Bowie Tupou.

He's been a bit less active since then, with a 2013 win over Andrey Fedosov and a pair of victories last year against Artur Szpilka and Mike Perez, his first two fights on HBO with new promoter Gary Shaw. He's also built a decent fan base in the northeast, fighting in Philadelphia (his hometown), New York, Brooklyn, Atlantic City, and Newark in recent outings as his profile has gotten bigger.

At "just" 6'3", Jennings will have the same height disadvantage that most do against the 6'6" Klitschko, but Jennings also has a very long 84-inch reach, three inches longer than Klitschko. Jennings is a confident fighter, too, and his last three wins have all been quite solid, and should have him as prepared as he's going to get.

That said, he's also facing the usual long odds, and few expect him to seriously challenge Wladimir. Bovada currently has Klitschko listed as a 16-to-1 favorite, and Jennings as an 8-to-1 underdog, which seems fair. As easy as it is to look forward to this fight, because Wladimir is the top guy and Jennings is a perfectly legitimate challenger, it doesn't seem as though many take Jennings seriously as a potential upset candidate. But nobody took Buster Douglas seriously, either. Different situations, of course, but in boxing you never truly know until you know, at least at this level. 99 percent certainty isn't 100 percent, and Jennings got this fight for a reason. He's earned it.

Deontay Wilder

Wilder, 29, is perhaps the most intriguing potential Klitschko foe in the last near-decade. At 6'7", he's slightly taller than Wladimir. With his 83-inch reach, he's got Wlad beat there, too. And he hits like a monster, scoring 32 knockouts in 33 wins, and showing that power wasn't fake in his one decision, January's wipeout of Bermane Stiverne that saw Wilder claim the WBC heavyweight title, the only major belt not in Wladimir Klitshcko's possession.

For years, it has been easy to doubt Wilder (33-0, 32 KO) and consider him a potential fraud. His level of competition was often downright embarrassing -- probably never worse than in 2012 when he beat up a retired former middleweight who hadn't fought in five years and was nearly a foot shorter than him, and frankly wasn't that impressive in doing so.

But Wilder proved that there may indeed have been a method to his team's madness. Let's not forget that when Wilder won the bronze in Beijing back in 2008, he was all potential and raw ability that came from his size. Wilder didn't start boxing until 2005, right around the time he turned 20. In 2008, he was an Olympian, and a medal-winning Olympian at that.

He was also not physically developed. When Wilder turned pro in November 2008, he weighed in at 207¼ pounds. He was as lanky a heavyweight as you're ever going to see, looking more like a lean shooting guard than a professional boxer. His team was smart enough to understand that they needed time to build not just his skills, but his body.

Today, Wilder is comfortable around 220-230 pounds, and has matured into what appears to be a good all-around fighter. Stiverne was able to stand up to his heavy shots, but Wilder didn't get stupid and make the big mistakes that Stiverne seemed to be waiting on, and in the end, he showed he can go 12 rounds, cut a pretty good pace while doing so, and be just as effective as he is when smashing guys on the first good right hand that lands.

If Wilder wasn't floating your boat as a potential conqueror before that fight, he may have changed your mind with how he conducted himself in the ring on January 17. It was a very strong performance, and one that puts him right in the mix to be considered the top threat to Klitschko out there. When you combine that win with his physical tools, he looks dangerous.

Tyson Fury

Fury, 26, has been dancing around the outskirts of true heavyweight relevance for a while now. Maybe "relevance" isn't the right word -- given his box office ability, his excellent self-promotion, and his size, Fury is certainly a relevant heavyweight.

But let's also not get anything mixed up here. With one win over Bermane Stiverne, Wilder clearly passed Fury in terms of what they've achieved in their careers. Fury (23-0, 17 KO) has been knocking off mid-tier or worse heavyweights for about four years now. A pair of early career wins over John McDermott are every bit as credible as most of his recent victories, given where he's at in his career, and his 2011 victory over an out of shape Dereck Chisora may still be his best to date.

One thing Fury and his team do well is talk up non-challenges as significant risks. Even his next fight, set for February 28 against also-ran Christian Hammer, has been titled "Risky Business" on the promotional posters. Other than the fact that heavyweight fights can turn out to be shocking results just on one big punch, Hammer (17-3, 10 KO) is no true threat to Fury, and the same was true of the likes of Neven Pajkic, Martin Rogan, Kevin Johnson, Steve Cunningham, and last November's washed-up rematch version of Chisora. All were sold as potential derailing foes. None were, though Cunningham certainly gave his best before Fury was able to use his enormous size advantage to wear him down and knock him out.

But as easy as it is to pick at Fury's record and find big holes where results are supposed to be, Fury has really put in work to become a serious fighter, too, and has made massive improvements over the years. Whereas he was once the big British guy with the extremely cool name who uppercutted himself in the face, Fury is now a fighter who has learned that is size doesn't just lend itself well to knockout power, but to keeping opponents comfortably at bay. He still has defensive lapses, but Fury, at 6'9", has begun to rely much more on his jab and his surprising agility. He generally keeps a strong workrate and can dominate a fight purely with activity from the outside. And he can punch, too.

It seems like Fury has been on the scene for a long time, and he has. He turned pro in late 2008, just like Wilder, but he also has been talking himself up from the very beginning. Some consider his style of self-promotion annoying, and surely he can be a bit off-putting and arrogant at times. But he's also still very young. At 26, Fury is a few years younger than Wilder, and figures to not even have entered his true prime yet. Like Wilder's team, Fury's has been calculating about the way they've moved him, and both of those camps also understood that there would be critics, and that for their fighter, the best thing to do was ignore them and go about the business at hand. Fury continues to do that, staying active and waiting, perhaps, for the right time to strike. Given how smart Fury and his team have been thus far, they just might know exactly when to go for the gusto.

Anthony Joshua

"He's built how a champion should be, is the right weight, very strong and technically capable. He's also very down to earth and asks a lot of questions - that shows the man wants to learn. He has a good future if he keeps doing what he's been doing."

That's Wladimir Klitschko on Anthony Joshua, the London 2012 super heavyweight gold medalist who sparred with the champ last year. At 25 and just getting his pro career started, Joshua (10-0, 10 KO) has the looks of a possible future king. There's really no doubt about that. He's 6'6", comes in at a ripped 235-240 pounds, has good skills that are sure to keep improving if he stays focused, and has shown concussive power. Nobody -- even some pretty durable veterans -- has been able to survive past round three with him thus far.

That will change, of course. It always does. Eventually, you find out that there are guys out there who can take your punch. Wilder just did with Stiverne, and Wilder proved he was more than a single right hand or a lone big offensive assault. Joshua still has those days ahead of him.

The question now is whether Anthony Joshua will become a serious contender, or if something will derail him. Just a couple of years ago, David Price looked like a "next big thing" sort of prospect. He's now trying to rehab his career in Germany after a pair of TKO losses to Tony Thompson. And maybe Price will find his rhythm, learn from the defeats, and come back from those losses. Wladimir Klitschko did it. But a lot more guys don't come back and become world champions than do in that situation. Klitschko is special. That's why we're trying to figure out what young fighters might possibly ever be able to beat him as he closes in on 40 and seems just as likely to get tired of the sport and retire as he is to ever lose again.

Joshua has a lot to prove still, but it's easy to see why he gets people excited. He passes the eye test with flying colors. By all accounts, he's a hard-working, level-headed young fighter who understands that there's much more to be done. He's not gotten ahead of himself. And against the right opponents, he's done his job thus far.

If Joshua is the man to someday beat Klitschko, Wladimir will be at least in his early 40s, so we're talking three or four years from now. But given Klitschko's fitness and commitment, plus the relatively tiny amount of damage he's taken in his career, it's possible that will be the fight in a few years. Joshua has to get there, though, and there's a lot of ground left to cover.

Vyacheslav Glazkov

Glazkov, 30, is included here because I feel it's only right to include him as an unbeaten younger fighter still climbing the ladder. He also makes for a nice, even five fighters listed, and I felt he was a better choice than Dominic Breazeale or Andy Ruiz Jr.

Glazkov is not an A+ fighter. He's not an A+ prospect. He's a B at best, perhaps. A good fighter, well short of great. He was lucky to get a draw result against Malik Scott back in 2013. His best win to date is probably a March 2014 victory over a shot Tomasz Adamek. He's got a collection of decent wins, but nothing that stands out. And he might not even keep his undefeated record a month from now when he faces Steve Cunningham on March 14 in Montreal.

Glazkov (19-0-1, 12 KO) is a workmanlike fighter. The Ukrainian, now based in Fort Lauderdale, Florida, goes out and gets his job done. That's what he's been so far in his career. That also makes him a contender in today's still-depleted heavyweight ranks. Of these five fighters, Glazkov is perhaps the darkhorse. Joshua is further off and if the two of them met in a month, Glazkov might well beat him largely on experience. But Joshua has the sort of upside Glazkov does not appear to have. This might be as good as Vyacheslav Glazkov gets.

The Other Option: Nobody

It's not hard to imagine a day in the near future where Wladimir Klitschko decides that enough is enough. His main goal now appears to be unifying all four of the major heavyweight titles, and Deontay Wilder's WBC belt is the only one he does not have. That belt was previously vacated when older brother Vitali Klitschko decided to leave the sport and go into politics.

Wladimir is a new father. His family life is going to consume more of his time, and he's a famously dedicated professional boxer. If there comes a time where Klitschko feels that he can no longer put the same focus into his career, he could just go ahead and bow out, never adding that fourth loss to his record. He's made a ton of money and has the potential to make a lot more as a promoter.

At most, Klitschko probably has five years left in the sport. Will anyone be ready to take him down by then? Will the field be able to catch up to him? More than figuring out who might be able to beat him, the bigger question could be if he can be beaten before he gets tired of the grind.