This is one of two temple guardians: Misshaku Kongo and Naraen Kongo.
Temple guardians are placed at the entrance to a temple to ward off evil. Each of these figures holds a vajra for crushing ignorance. Their open and closed mouths represent a and un, the first and final syllables of Siddham (a script used to write Sanskrit): these syllables symbolize all spoken sounds and scripts, thus all knowledge. Worshippers who enter the temple precinct through the guardians’ gate symbolically acquire this knowledge.