The death of James MacDonald Hudson, the Canadian superhero known as Guardian, was one of the most shocking moments of the first Alpha Flight series. As the team was battling with the evil group known as Omega Flight, Guardian - the leader of Alpha Flight - is destroyed when his battlesuit explodes, leaving his widow to lead the team. It was an exceptionally well-written death that made Alpha Flight one of the must-read books of the late 80s.
Of course, since this is comics, Hudson didn't really die (even though we saw his charred corpse). He was really teleported to one of Jupiter's moons, where an alien race gave him a power upgrade. He returned to Earth to rejoin his former team before dying again - but not really dying, just teleporting somewhere else - and then really dying.