A 49-year-old retired boxer is trying to pick a $115 million fight with Mike Tyson -- claiming "The Hangover" star hijacked his "Iron Mike" nickname 25 years ago.

The other "Iron" man is Mike Landrum -- a former professional fighter who claims he coined the nickname "Iron Mike" before he turned pro in 1983. Tyson started fighting professionally in 1985.

Landrum has filed a lawsuit in federal court in Los Angeles, claiming he owns the trademark to the nickname "Iron Mike" -- and therefore, Tyson infringed on his rights by using the nickname throughout his boxing career.

Landrum -- who's representing himself in the case -- tells us he was "hindered from getting any major title fights or sponsorships because of the name confusion."

For the record -- Landrum's record was 6-4 as a pro.