Not sure. There was speculation that it was from a Kung Fu episode - https://www.imdb.com/title/tt0623181/ but the actual costume is different.

Possibly this costume was based on that, or maybe just inspired by it.

Anyway, here's the costume.

https://abracadabranyc.com/products/devils-champion-leather-armor-set

Regarding the choice: my opinion is that this choice was Elon trolling. I mean, how troll would it be to dress up in the devil's uniform when you are poking fun at and destroying the political satanist elite?

Part of this view is informed by the speculation that Elon has been working with the white hats for quite some time, and there's a good amount of evidence for that.

I see it as Elon's sense of humor and ultimate troll; a 'fuck you' to the satanists. "Look, I'm "the devil's champion"! Suck eggs while we destroy you!!"

Another factor is that this was a halloween costume choice by Elon, BUT he then turned around and used it for his profile on X when he took over twitter.

If you think the black hats are going to just allow some guy come along and acquire their most important information control system, you'd be wrong. So how did Elon take it over? I can't see any other way except planned, white hat work, where the Cabal were helpless to stop it. because the Cabal should have many more billions and trillions of money at their disposal. But they couldn't even stop a 'takeover' by Elon. So the question is, why not?

I'm fiercely God centered and have been practicing my faith for decades, but I'm not fazed at all by this choice by Musk. Seems perfectly in character to me. Good character.

$0.02