There is a little known Halacha that the Gemara alludes to in מסכת ברכות. Rabbi Yochanan rebukes Rabbi Zeira for complaining that he’s forced to bring a gift to the king.
Rabbi Yochanan tells him that one should always try to receive one of the kings of Israel. And he should even try to receive or greet a king from the nations of the world. For if one merits life in עולם הבא and he sees the מלך המשיח, he will see the contrast between a holy king and one who is not.
This is brought down in the Shulchan Aruch as a Halacha that the Yerushalmi says applies to leaders of countries. The Rabbis even instituted a ברכה to be said upon seeing a king, and is even found in the Artscroll Siddur.
We were once in Eilat when the king of Jordan arrived there. Many made reference to this Halacha of ראיית פני המלך, seeing the face of a king.