According to multiple reports, Steinbrenner -- who turned 80-years old on July 4th -- was rushed to St. Joseph's hospital in Tampa where he was later pronounced dead.
Steinbrenner -- a U.S. Navy veteran -- retired from running the Yankees in 2006 ... leaving his sons Hank and Hal to run the team.
Since Steinbrenner took over the team in 1973, the Yankees locked up 11 pennants and 7 World Series titles.
Among Steinbrenner's many accomplishments -- his famous "grooming policy" ... in which players and coaches are not allowed to sport hair past their collar ... and the only acceptable facial hair is a mustache.
UPDATE: A rep for the Steinbrenner family has released a statement saying, "It is with profound sadness that the family of George M. Steinbrenner III announces his passing. He passed away this morning in Tampa, Fla., at age 80."
The rep adds, "Funeral arrangements will be private. There will be an additional public service with details to be announced at a later date."