Efreeti Chain is a legendary item, but I’m having trouble finding its lore in D&D. Anyone knows where I can find some? Who made it and who possessed it?

I don't know that it has specific lore? None that I've read of, anyway, or can find with a quick google search.

Even if it does, there's nothing stopping you from making up your own. Perhaps some powerful archfiend ordered it made for themselves and infused the souls of efreeti into it to empower it.

But it's for sure not a chain mail an efreeti wears, isn't it? Mostly likely it's an efreeti's essence trapped in that red gem on it's chest, right?