In the first issue of James Robinson's run of Justice League of America, issue #38, we see D-List hero Blue Jay heroically try to warn the Justice League of an impending new menace. Blue Jay dies in this effort - but it made me recall all the other heroes who die trying to sound the call of an oncoming crisis. Wether they where successful in their warning or not, here are the ones I best remember.
These are the only ones I can readily think of off-hand. If you recall any other heroes who died trying to warn everyone of danger - then feel free to contribute and leave a message.
Blue Beetle (Ted Kord)
Ted famously gave his life in the opening preview issue of Infinite Crisis. Ted was trying to put the pieces together of an on-going mystery threatening the DCU. Despite his efforts nobody was actually listening to him. So, going it alone, he went to confront the mastermind who was working behind the scenes. It was non-other than Justice League backer Maxwell Lord, who was revealed to not only know every Super Hero's secret identities - but had high-jacked Batman's Brother Eye Satellite to create an army of OMAC Meta-Human Killers. Ted found all this out, and got a bullet right in his face for his trouble. His final defiant message "Rot in Hell, Max." was not lost on the readers. While Blue Beetle did die, his death helped signal the other heroes of the upcoming crisis, as Blue Beetle's shot-apart goggles managed to reach Batman and the Justice League. A lesson in not ignoring your friends when they need help.
Mr. America II (Trey Thompson)
In the pages of the newly relaunched Justice Society of America, Mr. America arrived at a murder scene to help the FBI. When they said they needed to notify the next of kin, Mr. America took off his mask and said they already knew, as it was his family who was killed.
So Mr. America went on the hunt for the killer, and found the origin of the threat - Vandal Savage, who was attempting to wipe out the blood-lines of all the heroes. Mr. America was then murdered, but before dying managed to crash through the sky-light of the JSA's meeting room, and die right on their table, giving them warning of the threat against them.
Oh, and as for trying to kill off the Mr. America blood-line, Trey's FBI partner, Jeffrey Graves, took over for his friend and serves in the JSA.
Flash (Barry Allen)
This is a weird one - where Flash did indeed give warnings to his friends and fellow heroes of the danger ahead - and did later die. I'm not positive wether that all happened at the same time - relatively speaking - given all the rips in time Flash was appearing in to give the news. But he did Warn people, and then died. So, does he count on this list?
Orion of the New Gods also heralded the end of things and died for his trouble. In the Final Crisis series, Orion washes up on the docks and dies, with the warning that "They" did not die, and that "He" was in all of them. Orion died for his trouble, but his dead body helped get the League on the case - only eventually to find out that Darkseid had indeed not died (along with all the other New Gods) and that he was indeed inside all of humanity - corrupting Earth and it's people from the inside out. Darkseid, evil, had won. With the heroes on the case, though, Darkseid's reign over Earth wasn't a long one.