Jagi's the third of the four Hokuto brothers, and honestly, he's a piece of work. He's willing to do whatever it takes to win—dirty tricks, underhanded tactics, you name it. He tried to kill Kenshiro early on and got his face absolutely destroyed for it, leaving him badly scarred. That's why he wears that iron helmet; he's hiding what's left of his head.
The thing is, Jagi never gets over his hatred for Kenshiro, and he actually sets some major plot points in motion because of it. But here's the weird part: once he dies, fans and even the story itself kind of forget about him. When people talk about the Hokuto brothers, Jagi rarely comes up.
Content compiled by AnimeList.moe from publicly available sources.