I would say Hulk Hogan and John Cena are just about tied, with each having seven years on top. I would say Hogan became "the man" in 1985, and remained the biggest element of WWF programming until the summer of 1992, when he became more of a part-time wrestler. Cena became the man in 2005, and in my mind has been the face of the company ever since.
Of course, one could make the argument that Hogan was on top until the night he left the company at King of the Ring 1993, seeing as he was still champ and all. I just don't view a guy who refuses to wrestle on regular television to be the focal point of a wrestling company's product.
slight correction, Hogan became "the man" February 1984 thats when he beat the Iron Sheik for the WWF Heavyweight Title. and other then 18months when he didn't have the title and was frequently absent, he was still the face of the company for 6 years and then a further year roughly between WrestleMania 7 and 9 and what happened everytime he returned? he was immediately "the guy" to get the biggest pop again whether he was be a second for someone, he was in the main event or midcard matches or even just making a suprise appearance.
In other words Hogan will always be the biggest name to come out of WWF/E in history,
now if you are talking about longest run as the main focus during WWF post 1984 then it would be between Hogan and Cena both having held the titles and been on the winning end of Main events for the better part of 6-7 yrs.. unless you wanna count Hogans run in WCW which he was the face of the company for another 2-3yrs b4 Goldberg and the nWo
Austin and Rock aren't even close. Austin was only around for 4yrs as a full time face of the company. The Rock only competed for 7yrs. and Triple H was the face for around 4 straight yrs then on and off after that
now for the real answer, if we are talking about WWE (WWWF, WWF and WWE) total history. 2 names cement the spot as the longest running focus of the company, Bruno Sammartino and Bob Backlund
Bruno held the WWWF title for 8 straight years as "The Guy" (1963-1971) and Bob Backlund was "The Man" and champion for 6 straight years leading upto the soon to be Hulk Hogan returning as a face and capturing his first world title.
So there ya go let's have a fatal fourway between Hogan, Cena, Sammartino and Backlund....