Without a doubt, wrestling's biggest icon ever has to be Hulk Hogan. But since you said WWE only, I have to leave out how he helped WCW to their biggest run ever and set a few records there, how he was the leader of the most marketable heel group ever known as the NWO, how he was a top attraction everywhere he went (WWF, WCW, AWA, NJPW), how he got some of the strongest crowd reactions ever on BOTH sides of the fence (the fans loved him so much in the AWA that they nearly rioted when he didn't win the title, and he made the fans hate him so much in WCW that they belted the ring with garbage on a nightly basis), etc.
Ok, I'll just stick with the WWE.
He was the one the WWF was built on when it decided to go national. He was the one who helped make the WWF into a strong brand name. He was the one in the main event of what is said to still be the most iconic event ever in wrestling, which is Wrestlemania 3, an event that also drew the largest North American wrestling crowd ever (93,173). He was the one who drew the biggest rating ever in North American wrestling history (33 million people in February of '88.) He got the loudest and longest ovation at the Hall Of Fame ceremony as I recall it. He's the one name every knows, wrestling fans or not.
Several wrestling legends also have had their biggest career moments (or one of them) when they were in the ring with Hogan. Andre is a legend and his most memorable and replayed moment is getting body slammed at Wrestlemania 3 by Hogan. Roddy Piper was drawing nuclear heat with his feud with Hogan, which was at the center of the original Wrestlemania main event. (WCW was not ashamed to exploit this feud in WCW, as it was what Starrcade 1996 was centered around and was WCW's biggest PPV buy rate ever until Starrcade 1997 a year later.) Paul Orndorff was also in the main event of the first WM with Hogan, and also had what was a shocking heel turn back then when he turned on Hogan. The two of them went on to break attendance records in the summer of 1986, drawing 74,000 plus for The Big Event, a number larger than anything Austin ever drew at his peak. Randy Savage's drawing power was at it's strongest when he played the heel during The Mega Powers break up angle in 1989, with Wrestlemania 5 doing a huge buy rate for back then, and also setting financial records for the company that were not broken for several years. Ultimate Warrior's biggest career moment? Holding up both the World and IC Titles after being the first man to defeat Hogan cleanly since his Hulkamania run began in 1984.
If you want to talk about WCW, Sting's drawing power was its most intense when he feuded with Hogan and the NWO. Goldberg was the one big star they made during that period (he was as hot as Austin and Rock were at his peak) and his biggest moment was defeating Hogan in front of the largest Nitro crowd ever, doing one of the biggest rated segments ever during the Monday Night Wars.
As for Austin saving a dying company, Hogan's popularity was so intense that he could have easily done the same thing if the company was in that dire of shape when he became hot. Vince poured every dollar he had into the first Wrestlemania and then some and has said many times since then that if it hadn't been the success that it was, he would have gone out of business. And Hogan was a huge part of what made it a success. I'd have to believe this is a similar claim to helping a company stay afloat as the one Austin can make. Hogan went on to help establish Wrestlemania as a household name and a spectacular event (especially with the iconic Wrestlemania 3) for almost the next decade.
