3 youngest (and 3 oldest) WWE Champions of all time 

#2 Youngest WWE Champion: Yokozuna (26 years, 6 months, 2 days)

Yokozuna wins WWE title

Due to his sheer size, Yokozuna was as perfect of a replacement for Andre The Giant as WWE could have gotten at that point in time. Yokozuna weighed around a whopping 600 pounds and Vince McMahon decided to turn him into a top heel in WWE.

Yokozuna won the Royal Rumble match in 1993 by eliminating Macho Man Randy Savage in the end, and bagged a shot at Bret Hart's WWE title. He defeated Hart at WrestleMania 9 to become the youngest WWE Champion ever, but didn't get to keep the belt for long, as Hogan came out to save the day and ended up winning the title.

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#2 Oldest WWE Champion: Hulk Hogan (48 years, 8 months, 10 days)

Hogan vs Triple H

Hulk Hogan came back to WWE with the nWo in 2002. He faced The Rock at WrestleMania 18 in one of the biggest matches of all time. The ovation he received that night convinced Vince McMahon that Hulk was still incredibly popular among the fans. This resulted in Hogan getting a WWE title run.

At Backlash 2002, Triple H defended his newly won WWE title against Hogan. After interferences from Chris Jericho and Undertaker, Hogan managed to pin Triple H to become a 6-time WWE Champion.