This is probably going to be too easy:

Who was it that gave Jean Loring the black diamond of Eclipso ???

The Spectre.


...

I'll guess it was Black Adam.

Nope. She used it to turn into Eclipso then went after the Spectre and seduced him into going after everything magical, but he didn't give the diamond to her.

No. No member of the Marvel Family, or Black Marvel family member, gave her the diamond. You may be thinking of the time Black Adam gave Mary Marvel her powers since she'd lost hers and Jean as Eclipso got in tight with her and turned Mary evil to the point where Mary did the nasty with Darkseid.

I read this story, but it was so bad my brain has rejected the details of it.

Felix Faust?

Dr. Thaddeus Bodog Sivana? (To this day I can't read his dialogue without hearing Howard Morris' voice.)

As campy as that show was he was PERFECT as Dr. Thaddeus Bodog Sivana!!!

Nope, none of those people.

This person gave Jean Loring the Black Diamond in her cell in Arkham because Alexander Luthor made this person do it.

Calculator?

I have no idea.

--wyld

Psycho Pirate did it

Totally off-topic here: I've long had a half-formed theory about Dr. Sivana's children.

As most comics fans know, Sivana had four children: Magnificus and Beautia, who are the Olympian ideals of physical perfection; and Thaddeus Jr. and Georgia, who look uncannily like their dad.

My theory is that one set of kids are his biological children, while the other are lab-grown clones that he tweaked to come out exactly how he wanted. The theory is half-formed because I can't decide which set makes more sense to be the clones; would Sivana strive to create ultimate physical specimens a la the Master Race, or would his colossal ego lead him to create near-physical duplicates of himself?

I thought their mom was perfect/beautiful, and two kids took after their mom, two after thier dad.

Not him either it was...


Damn it. And here I was about to point out that Monday's "Pearls Before Swine" would be a hint.
On that note, let me just say, Pirates make lousy Dry Cleaners.

Yes, Psycho Pirate, who was killed by Black Adam in a most undignified way, did indeed toss the Black Diamond into the cell with Jean Loring.

And, don't forget kids, Psycho Pirate is back in action as a Black Lantern.

Anyhow, Vamroc has the thread.

Well, that may be the post-Xerox Hour explanation. Pre-Crisis it was never explained; actually, I think his Aryan-perfect kids, from the very early stories, were completely forgotten about when they brought in the lookalikes sometime in the mid-40s, and only brought back when DC acquired the characters.

Your explanation makes more sense, but mine is more comic-booky fun!