No fighter in history is/was unbeatable, least of all Tyson. Virtually everyone in the Hall of Fame was beaten in or near their prime, had tough fights with lesser opponents, and even the select few who kept their 0 had close calls.
Unfortunately, opinions of Tyson are always extreme. He's either the greatest ever or no better than a club fighter. Lewis, Bowe, Johnson, Dempsey, Klitschko, Langford, Foreman, Holyfield, Liston, Patterson, Quarry, Walcott, Corbett, Shavers and Louis were all beaten (and in many cases KO'd) by lesser fighters than Tyson, but of course he'd have no chance against them.
Unfortunately, opinions of Tyson are always extreme. He's either the greatest ever or no better than a club fighter. Lewis, Bowe, Johnson, Dempsey, Klitschko, Langford, Foreman, Holyfield, Liston, Patterson, Quarry, Walcott, Corbett, Shavers and Louis were all beaten (and in many cases KO'd) by lesser fighters than Tyson, but of course he'd have no chance against them.

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