#2 Bob Backlund (WWE title reign: 2135 days)
On February 20, 1978, Bob Backlund ended Billy Graham's 296-day World title reign to become the new WWE Champion. A year later, he lost the belt to Japanese legend Antonio Inoki and won it back in a rematch on December 6, 1979.
The rematch was declared a no-contest due to interference by Tiger Jeet Singh, and Inoki remained the champion. He refused the belt though, thus making it vacant.
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Backlund went on to defeat Bobby Duncum for the vacant belt. Vince McMahon's promotion doesn't recognize Inoki's World title reign as a part of its official history. Bob Backlund lost the title to The Iron Sheik on December 26, 1983, with his reign clocked in at 2135 days.
#1 Bruno Sammartino (WWE title reigns: 2803 days, 1237 days)
On May 17, 1963, Bruno Sammartino submitted Buddy Rogers at an MSG house show to become the second-ever WWE Champion in history, thus kicking off quite possibly the most impressive World title reign in all of WWE.
Sammartino held the title for a whopping 2803 days before dropping it to Ivan Koloff on January 18, 1971. Sammartino's second title reign would come two years later with a win over Stan Stasiak. Bruno held the title for 1237 days this time around, before eventually dropping it to 'Superstar' Billy Graham.