The name says it all here. Blue Devil is Dan Cassidy, a stuntman who, while wearing a blue demon costume on the set of a film shoot, is attacked by an actual demon whose magic fuses him to the demon suit he’s wearing. Fearing he will be stuck in the exoskelton forever, Cassidy sought ways to separate it from himself. Eventually he makes a deal with the demon Neron which transforms him into an actual demon.
A side effect of the unnatural fusion of magic and technology turns him into something of a magnet for supernatural occurrences. And Cassidy soon finds himself a reluctant superhero as he combats them. He eventually ends up with a spot on the Justice League roster.
Blue devil aka Dan Cassidy uses a trident as his weapon. Originally it was a mechanical device that he designed and built himself. He later acquired the magical “Trident of Lucifer” which is the current weapon he uses today.
Blue devil first appeared in Fury of Firestorm #24 (June 1984). That story leads directly to his title comic released in 1984 Blue Devil #1.