This will not be a popular opinion on the internet. But, I believe John Cena has had the greatest run of any WWE superstar in the history of the company.
Better than Hulk Hogan, better than "Stone Cold" Steve Austin, better than The Rock, better than Bruno Sammartino, better than everyone.
Cena debuted in 2002 and is entering is 15th year in the company. For his entire 15-year run, he has been at or near the main event. He is one of the only superstars on the current roster to elicit a thunderous ovation, whether it be positive or negative, every time he runs down to the ring. He has to be the most polarizing figure of all-time too. Most crowds are split 50-50 in favor or against him. Depending on what city they're in, it can fluctuate to be more negative or more positive.
I also see him as the greatest of all-time because of how long he has been on top. Cena won his first WWE Championship at Wrestlemania 21 in 2005. Now, in 2017, he is going for his record-tying 16th WWE Championship win at the Royal Rumble on Jan. 29. He is in his 12th year of being on top as a main event talent. Hulkamania ran wild in the 80s but it peaked between 1985-1988. Hogan was gone from the WWE by 1993. Although the Hogan era was important to establish the popularity of WWE, it didn't last as long as Cena.
"Stone Cold" Steve Austin is probably the most popular superstar ever. His era, The Attitude Era, was the hottest time to be a wrestling fan. More people were watching wrestling on Monday nights than Monday Night Football. However, the edgy programming shift that was The Attitude Era, only lasted from 1997-2001. Austin moved the needle more than anyone, but he was in-and-out of the WWE very quickly, entering in 1996 and exiting in 2003. The Rock's career pretty much coincided with Austin's. The Rock debuted in 1996 and was gone by 2004. He was one of the most influential characters in the middle of the greatest period in WWE history. But neither Rock nor Austin had the longevity that Cena does.
Bruno Sammartino had the longevity that Cena has. He was the champion from 1963-1971, and then again from 1973-1977. That will never happen again. However, the landscape of WWE was very different in those times. Sammartino was basically only wrestling at Madison Square Garden since WWE was strictly a New York territory at that time. Under Cena, the WWE is a global entity. Sammartino didn't nearly have the schedule that Cena does. For example, Cena goes from his home in Tampa, to WWE Live Events in Corpus Christi, TX, to San Antonio, TX, then SmackDown in Houston, then to New York to host the "Today" show, then to Beijing to promote the WWE at a media appearance, then to Los Angeles to host an award show, then to wherever the set is for his latest movie. He has had a schedule like this while maintaining his status as a top WWE superstar.
He's even found the time to grant more wishes than anyone ever for the Make-a-Wish foundation. To accomplish what he has accomplished both inside and outside of the ring while having the longevity that he has had, makes him the greatest of all-time. Sure, "Stone Cold" probably sold more t-shirts than Cena has, and Hogan probably created more fans, but Cena has accomplished more than any superstar. He is a 15-time world champion, and will likely tie Ric Flair's record of 16 this year. He has won every championship in the company, except the Intercontinental championship. He's won the Royal Rumble match and the Money in the Bank ladder match. He's main evented Wrestlemania multiple times. Not to mention all of the classic matches and rivalries he as been apart of. And nobody has been on top for longer on the scale that he has. Whether you like it or not, John Cena is the greatest of all time.