[The Australian Panther]

An interesting character indeed.
I note that at only once did Dr Diamond appear on the cover. A sign that someone wasn't impressed by the character?
Also, the character he has most in common with, is the DC Villain ECLIPSO, who if I remember rightly uses Black Diamonds to make people villainous.
There was also a Western Hero called Black Diamond.
https://comicvine.gamespot.com/black-diamond-western/4050-1253/
AC comics took the name for a female hero - apparently earmarked originally for a movie starring Sybil Danning, the 4 issues noteworthy for Paul Gulacy's covers.
https://comicvine.gamespot.com/black-diamond/4005-48285/

The comics industry can be very incestuous, can't it?

Link to the book: Dr. Diamond Complete Collection

[FraBig]

Yes, he's similar to Eclipso, but he's also very similar to a Timely (Marvel) character that debuted around that time (same period of 1941): Blue Diamond.

Both Blue Diamond and Dr. Diamond are men of science (an anthropologist and a surgeon) that get involved in a shipwreck and somehow get in contact with peculiar diamonds: Blue Diamond's one will explode and make his body diamond-like, while Dr. Diamond's one is a mystic artifact.