He is HIM

A phrase used to acknowledge someone who just perform an admirable feat.

It originated around 2016 in the online game League of Legends. A very high ranked NA midlaner, Pobelter, was known for very aggressive and skillful plays that would either succeed and enable him to carry the game or fail miserably.
He had a large amount of alt accounts that used a similar playstyle, and teammates and opponents would often see those and wonder "is it him?", referring to Pobelter on an alt.

The phrase quickly gained popularity throughout the ladder and on streams, and would end up being asked of anyone who made a nice play, eventually switching from it's original question form to the proclamation that, indeed, he IS him.

*dude is about to flip the bottle*
Everyone: Oh oh oh, is it him???
*bottle lands upright*
Everyone: OH SHIT HE IS HIM!