LSH: Chemical King

Aside from its great size, the Legion of Super-Heroes has also stood out in the mortality rate of its members. And unlike other super-heroes, the Legion dead tended to stay dead, with a memorial statue in the Hall of Heroes, as shown here.<br />
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Although the LSH has been rebooted twice now, there has been no true new version of Condo Arlik, aka Chemical King. His power to create any known chemical reaction requires so much knowledge of science that he's probably too intimidating to write. So he has remained either killed off or unrevived.