Guess Who This Monster Athlete Turned Into!

Before this kid was shreddin' the gnar and grinding the skatepark bowls, he was just a novice rider ... boarding the San Bernardino Mountains and watching his dad surf the San Diego waves.

This slick guy appears to be a smiling fella ... however, he's deemed as a monster on the slopes, and has 5 Olympic medals to show for it! Even though he recently retired from his sport, he isn't afraid to show you on Insta that he's maintained his ripped figure.

Need one more clue? He made a cameo in "Friends With Benefits" with Justin Timberlake and Mila Kunis.