He's had his ups and his downs, but when he's on his game, few heavyweights have ever been more difficult to beat than Tyson Fury

There have been moments in Tyson Fury's career when he's been so good, so dominant, so on top of his game that one wondered if any heavyweight in history would have been able to defeat him.

When Fury, the unbeaten WBC champion, is both mentally and physically on his game, it's a stretch to think there's more than a handful of heavyweights who have ever lived who could compete on even terms with him. Muhammad Ali, Joe Louis, George Foreman, Larry Holmes, Mike Tyson, Lennox Lewis, Jack Dempsey, Rocky Marciano, Evander Holyfield, Vitali Klitschko, Riddick Bowe -- you name him -- and he would have had plenty of difficulty with a 6-foot-9, 270-pound heavyweight who can box, punch and move.

On Saturday in Riyadh, Saudi Arabia, it will be Oleksandr Usyk's turn to try to solve that puzzle. They'll meet for the undisputed title in Kingdom Arena in a bout streamed in the U.S. on PPV.com, DAZN and ESPN+.

The problem for Fury is that he hasn't always been on top of his game. His best performance was probably his 2020 stoppage of Deontay Wilder at the MGM Grand Garden in Las Vegas in the second of what become a three-bout trilogy. After fighting to a split draw in their first bout, Fury told everyone who'd listen he'd go straight at Wilder and knock him out.

While he didn't put Wilder down for the 10-count, he battered him from pillar to post and stopped him after seven one-sided rounds. He looked very much that night like the best pound-for-pound fighter in the world.

He stepped up on Nov. 28, 2015, in Dusseldorf, Germany, when he won a unanimous decision over Wladimir Klitschko to become IBF-WBA-WBO heavyweight champion. He won a classic slugfest in the trilogy fight against Wilder on Oct. 9, 2021, in arguably the best heavyweight bout of the 21st century.

Few men his size have had the agility Fury does, or the quick hands and the boxing ability. Combine that with a guy who is the size of an NBA power forward and it's a formidable combination.

Usyk, of course, shrugs the size difference between them off. Fury is six inches taller, has a seven-inch edge in reach and will be perhaps 50 pounds heavier. 

In an interview with DAZN upon arriving in Saudi Arabia, Usyk said, "He is big, tough, very big. But size doesn't matter. If size mattered, the king of animals would be the elephant."

For all of Fury's many successes, though, he's had just as many low points. None was lower than on Oct. 28 in Riyadh, when he was nearly upset by ex-UFC heavyweight champion Francis Ngannou in Ngannou's pro boxing debut. Ngannou put an unmotivated and out-of-shape Fury down in the third and nearly defeated him. Fury won a split decision in perhaps the worst performance of his career.

It isn't fair, though, nor is it wise to use the Ngannou performance as a benchmark, though. Fury was unmotivated and thought he'd make a multi-million payday for a few moments of work. Had he pushed himself in training to prepare, he most likely would have done to Ngannou what Anthony Joshua subsequently did on March 8, when Joshua knocked Ngannou out in the second.

He looked lean and fit upon his arrival, and that speaks volumes to the manner in which he prepared for the undisputed title fight. Usyk responded to Fury's condition by saying oddly that one loses weight when nervous. Fury beamed upon hearing that.

"I'm very nervous, Usyk," Fury shouted to the unbeaten unified champion. "Please don't beat me up on Saturday night. Please? Extra please?"

Fury is a -135 favorite to win at BetMGM, with Usyk at even money. And if both are in shape and fight their best, it's difficult to see how Usyk will be able to overcome the physical disadvantages he faces.

If he fires that jab repeatedly at Usyk, Usyk is going to have a pay a serious price for trying to get to his distance, in the middle range. Usyk is smart and a slick boxer, and he has a great chin, but eating those jabs all night will wear him down and let Fury take advantage.

Usyk is 21-0 as a pro and is third pound-for-pound behind No. 1 Terence Crawford and No. 2 Naoya Inoue. He won the heavyweight Olympic gold medal at the 2012 Games in London, then became undisputed cruiserweight champion. On Saturday, he's gunning to become the undisputed heavyweight champion.

Fury praised Usyk, but he's still oozing with confidence. He's a great talker -- he's a better talker than he is a fighter, and he's an all-time great heavyweight -- and so you can never be sure where he stands mentally just by listening to his public pronouncements. But he sure looks the part at this point, and his motivation to climb the top of the mountain seems high.

"Let me tell you, if I was fighting an old dosser on Saturday night who had five fights and lost them all, it would still be very important to me," Fury said. "Every fight I've ever had is important to me. Every fight I've had along the way: Four-rounders, well, I didn't do any four-rounders; six-rounders, eight, 10-rounders, any one of them along the way, they were all very important.

"I believe every left and right turn I've ever taken in life, every time I've fallen over, every time I have climbed back up, all of it was leading to this moment. It's destiny, written in the stars."