Jason Beere (Earth-616).
He appeared in Avengers #169, which was published in March 1978. Here’s his History from the Marvel Wikia, which matches your description almost completely:
Jason Beere was a wealthy industrialist, worth over 200 million dollars, and one of Tony Stark's major competitors. He was diagnosed with a terminal disease and given six months to live. Frustrated that his vast wealth would be unable to save his life, he decided that if he should die, the world must die with him. He used a portion of his wealth to implant a powerful neutron bomb within his chest. He also had a suit of armor built for himself, and then had three what-appeared-to-be bombs placed in three locations around the world: in Peru, among a bird-worshipping tribe; in the Arctic Circle, within the cave of an immense polar bear; and in Moscow, within a museum. Beere forewarned the Russians and the bird-worshipping tribe that American heroes would be coming to steal the bombs, and convinced them to make every effort to stop them.
Wearing his armor, Beere then broke through a wall at Avengers Mansion and ambushed the Avengers there: the Black Panther, Captain America, and Iron Man. He attacked them savagely, attempting to force them to kill him, but Iron Man succeeded in subduing and unmasking him. Beere threatened them that the world would die when he did, and warned them of four bombs around the world. Iron Man flew Beere to his Stark International facility, where he used his original chest plate to stabilize Beere's failing heart.
The Avengers went after the three bombs in Peru, the Arctic Circle, and Moscow, and succeeded in retrieving them. However, upon examining the ‘bombs', Iron Man determined that there were no explosives within them. The Avengers linked the three devices together, and they played out Beere's last message, revealing the bomb within his chest, set to detonate when his heart stopped. Iron Man then placed Beere within a cryogenic chamber, where his heart would be slowed, but would never stop due to the chest plate.
The Marvel Wikia doesn’t note any further developments in his story: there’s a footnote about his mention in Avengers: Roll Call #1, in which they comment on his situation:
The Avengers noted the irony that Beere feared to die young, but now might live forever: an Eternity Man.
but it doesn’t mention any other appearances, and I can’t find anything to suggest he shows up in any alternative universes or storylines.