Moonlight Mask’s identity has always been a mystery (which is why the Moonlight Mask persona is credited as being played by "?" in the original series).

Decked out in white tights, white & red cape, white scarf, yellow gloves & boots, dark glasses, face cloth and Indian-style turban (pinned with a "moon" ornament), Moonlight Mask is armed with a whip, two six-shooters, shuriken and moon-shaped boomerangs. He also rides a motorcycle.

However, only audiences know that Moonlight Mask could very well be detective Juurou Iwai who seems to disappear from his friends before the caped crusader rides to the rescue in his motorcycle! Even his comical assistant Gorohachi Fukuro, his friend Inspector Matsuda, and children Shigeru, Kaboko and Fujiko are oblivious to Iwai’s secret identity.

(Source: Wikipedia)