WWE just added a real-life ninja to its roster -- with "American Ninja Warrior" legend Kacy Catanzaro inking a deal to join the McMahon family biz, this according to Jim Ross.
Catanzaro made history in 2014 ... becoming the first female competitor to complete the Ninja Warrior obstacle course AND qualify for the finals -- AKA Mount Midoriyama.
The 27-year-old super-athlete had been training at the WWE performance center earlier this year ... and this morning, Ross announced that she has signed with the company and made it official.
The craziest part -- Kacy's 5-FEET flat and weighs less than 100 POUNDS .