Wladimir Klitschko of the Ukraine is fighting David Haye of Great Britain in a much-anticipated heavyweight title unification bout on Saturday at Imtech Arena in Hamburg, Germany (4:45 p.m. ET/1:45 p.m. PT, HBO).

Klitschko is the reigning IBF, WBO and Ring heavyweight champion, while Haye holds the WBA title. (Wladimir's brother, Vitali, is the WBC champion.)

The fight is widely regarded as the most significant bout in the heavyweight division since Lennox Lewis stopped Vitali Klitschko in 2003 -- and could go a long way toward unifying the long-fractured heavyweight title.

It's been more than seven years since Klitschko lost a fight. Over that span, the 35-year-old has emerged as the dominant force in the heavyweight division, taking on and defeating all comers. Yes, the division hasn't exactly been overflowing with talent during Klitschko's reign, but he's routinely fought the best of what's available.

Haye is a former cruiserweight champion who moved up to heavyweight in 2008 and immediately began harrying the Klitschko brothers for a title shot. Without question, Haye is the best challenge available for either Klitschko brother, given their understandable refusal to fight one another.

They were originally set to fight in Germany on June 20, 2009. Haye pulled out 17 days before the fight with a back injury, asking for a postponement that wasn't granted. (Klitschko fought Ruslan Chagaev instead.) Later that year, the London native abruptly backed out of talks for a fight wtih Vitali, fueling speculation he was ducking the Ukranian-born champs. Haye and Wladimir have danced around one another in the two years since, with Haye outpointing 7-footer Nikolay Valuev for the WBA title in the interim. Not until Klitschko issued a public challenge via YouTube did the sides come to terms for Saturday's fight.

A gifted trash talker, Haye is just the sort of headline-grabbing figure the languishing division needs. He's worn the severed heads of the Klitschko brothers on a T-shirt, told writers he'd beat up Jean-Marc Mormeck "like Rodney King" before a cruiserweight unification bout, and infamously billed his November fight with Harrison as a "public execution" to be "as one-sided as a gang rape by a pack of silverback gorillas." (And he was right.) Should he win Saturday, Americans will love Haye or they'll hate him, but they won't ignore him. 

Klitschko, 35, enjoys advantages in size, weight and reach against nearly every opponent he faces, but that's doubly true against the former cruiserweight. A decorated amateur and Olympic gold medalist, he is a highly cerebral, intelligent fighter whose biggest strength is a comprehensive understanding of his weaknesses. Klitschko's patient, obsessive brand of risk management may not win many style contests but it's difficult to argue with the results.

Haye, 30, is an explosive puncher (particularly with the right hand) whose speed and elusiveness have presented unique problems for the mid-grade heavyweights he's faced. He's spent most of the pre-fight buildup trying to anger Klitschko, hoping (it seems) to goad his opponent into abandoning his safety-first approach and fighting angry. Whether the ploy succeeds is one of the more intriguing questions circling Saturday's showdown.

Further questions surround both fighters' chins. Klitschko has been down 11 times in his career, including knockout losses to fringe contenders Corrie Sanders and Lamon Brewster that took him years to live down. Haye was starched by Carl Thompson in the fifth round of their 2004 fight.

The key to the fight will be whether Haye can get inside the piston-like jab at the foundation of Klitschko's success, a task much easier said than done. If Wladimir is allowed to settle in and establish the rythym, it could be a long night for the Bermondsey banger.

Oddsmaker William Hill lists Haye as a 7-to-4 underdog, while Klitschko is a 1-2 favorite.

Haye's best chance is to apply constant pressure early, put Klitschko on his back foot and test that chin. But that runs counter to his tendency to wait for his opponents' mistakes before exploiting them. Against Valuev, Haye promised a dust-up but spent most of the night making himself an elusive target and trying to nick a point here or there. That's a recipe for disaster against Klitschko -- a far more athletic and technically sound opponent than Valuev -- who will gladly cut off the ring and use his 82-inch reach to rack up points from long range. Look for Klitschko to settle in behind that punishing jab, sapping Haye's energy and will, and finish him off in the middle to later rounds. Klitschko by seventh-round TKO.

Join the conversation about Klitschko-Haye on Twitter.

· @mrdavidhaye (David Haye)

· @hboboxing (HBO Boxing)

· @ChrisMannixSI (SI.com's Chris Mannix)

· @BryanAGraham (SI.com's Bryan Armen Graham)

· @timdalhberg (Tim Dahlberg, Associated Press boxing columnist)

· @GarethBOXUFC (Gareth A. Davies, Daily Telegraph boxing columnist)

· @NYPost_Willis (George Willis, New York Post boxing columnist)

· @latimespugmire (Lance Pugmire, Los Angeles Times boxing columnist)

· @kieranmulvaney (Kieran Mulvaney, Reuters and ESPN boxing columnist)

· HBO's Jim Lampley, Larry Merchant, Roy Jones Jr. and Harold Lederman will be ringside for the main event and undercard.

· The referee assigned to the main event is Genaro Rodriguez, a Chicago native who has refereed four previous Klitschko fights (against Eddie Chambers, Corrie Sanders, Francois Botha and Derrick Jefferson).

· In addition to HBO's same-day replay Saturday at 9:45 p.m. ET/PT, the fight will be replayed Sunday at 9:15 a.m. ET/PT and Monday at 11:50 p.m. ET/PT.

MANNIX: More on the line than title during Haye-Klitschko heavyweight bout

MANNIX: Wladimir Klitschko doesn't lack for motivation in fight against Haye

PHOTOS: Lineal Heavyweight Champions (1885-present)

Wladimir Klitschko has 29 pounds on David Haye at Friday weigh-in