Mr. Byrne,

Can I ask what you made of this character? I never thought much of the character itself and the two Secret Wars series were never favourites, but when he was used in the actual FF comic I thought he worked very well.

Try a search...this has been addressed before.

He ended up forsaking all his power and making a machine-thing to transform him into a human baby that I think someone subsequently killed. Then later, it was revealed he was a cosmic cube that became a life form.

I think. I could be wrong on my details since it's been 20 years since I read any of that stuff.

It happened in this issue, in a story titled "Secret Wars 3".    I don't remember the full details, but the  Beyonder was revealed to be a cosmic cube, as Brian mentions. 

I believe the accident that created the Molecule Man also created the Beyonder??? and that what Molecule Man's power and the Beyonder were really two sides of the same cosmic cube. Which I guess Molecule man's accident had split in two or something.

So they agreed to come together and form the cube they were meant to be.  Of course Doom tries to interfere, and the Thing tried to wish for Universal peace, too late, which surprised Ms. Marvel (She-Thing), who thought he'd wish for them to be back to normal.

Anyway, I believe the Molecule Man showed up later on, so not sure what happened.

But OI think the Beyonder's cube formed into a female living cube that went exploring the universe.  I think.

Oh Yeah.  That girl living cube then showed up in Starlin's Thanos series.

He got mutated.  Sometimes it is called Pineapple Thing. I kind of liked it.  I think it happened in the second issue I read. He was stronger than regular old Thing, and of course, as even more hideous than before, it caused some further angst. It lasted about 2 years.

First appearance

Him and Ms. Marvel (She-Thing)

 New version v. new version. he actually beat the Hulk here for, supposedly, the first time.