THIS HAS NEVER BEEN REVEALED. I think he did it to himself

See also all the pictures of Superman breaking out of chains that provide no clues as to who put Superman in chains or how they did it.

Looks like SOMEONE has a flashback to write

This feels like perfect material for a Full Circle follow-up. Ryan, can you get Alex Ross on the line?

"We have all these amazing powers now. Quickly! I must test to see if we can make a living as circus performers!"

Kudos to him doing it out in public like that.

Reed's first thought when they got these powers was a stage magic act. Sue would get in a box and turn invisible. He'd perform amazing feats of escape artistry. That monster just attacked while they were practicing.

WHAT IF...that monster had interrupted Reed Richard's special alone time?