'Free Solo' Star Alex Honnold

Freeclimbing legend Alex Honnold -- the star of "Free Solo" -- is being hailed as a real-life hero after rescuing a fellow climber Sunday who fell off a famous rock formation in Yosemite.

Honnold was at El Capitan -- the epic 3,200-foot formation he impressively climbed WITHOUT ROPES in his documentary -- when something went terribly wrong.

33-year-old Emily Harrington -- a 5-time sport climbing champ -- lost her grip and fell from the formation while attached to her climbing rope ... suffering injuries in the process.

"I took a bad fall and pinballed a bit then somehow hit the rope w my neck," Harrington explained.

That's when Honnold and his pals sprung into action ... getting to Harrington…