So basically Urouge is the biggest GigaChad in the series. He's currently on the moon fighting Enel. See to reach the moon the ancient sky people took balloons, it was foretold in the ancient ruins. Urouge's tan skin, massive body which is the middle size between Lunarian and Sky people, hints that he's a Lunarian hybrid. It was said that Birkan's strongest knight fought against Enel and lost, and coincidentally Enel showed up just recently despite being in his 50s.

So what would a Smiling Monk worship? The sun god of liberation that brings people smiles. He's definitely a Nika follower. He's currently fighting Enel on the moon after taking the balloon terminal up, will unlock his Lunarian powers and come back as Luffy's own Whitebeard, a rival and equal. A man with near invincible Lunarian flame powers, a fruit that turns damage into raw strength, and the Birkan martial arts which was elite enough to fuck up Luffy, Zoro, and Sanji during Skypiea. Urouge is the Lunarian we see in the Elbaf mural.

Urouge is THAT guy.