Chemical element with symbol Ra and atomic number 88. It is extremely radioactive and appears in the chronicles as a self-luminous paint, as a treament for treating cancer and other wild and extraordinary uses. Also, as it is extremely rare, expensive, and difficult to find, it is sought after even more than gold or uranium.
It was first sought after by Zolar who had found a way to "perform such miracles as total disintegration and controlling the weather". He created with it a weapon that appears as fiery globes and dematerializes any people or objects it comes in contact with and leaves a silhoutte due to radium's "photographic qualities". Upon contact with Superman he comes unconscious and loses his powers momentarily.
Zolar had developed a "thirst for radium [that] drives him to any lengths to get it". Upon hearing that the lost city of Ulonda had a vast accumulated supply, Zolar attacks the city trying to steal it. While firing a globe-gun to Superman, the globes bounces back upon the villain leaving just a shadow silhouette. (Act No. 30, Nov 1940).