Source: 1st appearance in Superman's Pal Jimmy Olsen #31 (1958)
Type: Transformation
In 1958, DC hadn't yet used Quality's Plastic Man in any of their comics (and wouldn't until 1966), and Elongated Man was another two years away. That means Jimmy Olsen AKA Elastic Lad was DC's first stretchable hero! Like Ralph Dibny, Jimmy would opt for a purple costume. However, his very first appearance had him in green, which was Jimmy's usual color palette.
This is the result of Jimmy being splashed with "liquid kryptonite", and of course, a scientist's failed cure for kryptonite poisoning won't work on Superman, but it'll take away Jimmy's powers, no problem. It wouldn't be Elastic Lad' only outing of course. Jimmy gets elastic powers again in Jimmy Olsen #37, this time by mistakenly drinking Professor Potter's elastic serum, thinking was soda pop. (Mad scientists have to stop putting fizz in their formulas.) Jimmy uses it to cheat at baseball mostly.
It wears off in due course, but Jimmy'll wind up drinking or huffing the stuff every so often throughout the Silver Age. It even gets him honorary Legion of Super-Heroes membership!
The Legionnaires sure like their men, uhm, supple. Well, would you believe it was all a ploy to make Lucy Lane jealous back in the present? Of course it was.
By the Bronze Age, Jimmy wasn't turning into Elastic Lad quite so often, though it could be fun for nostalgia's sake. Jimmy would in fact become Elastic Lad for the last time in the last pre-Crisis Superman story, "Whatever Happened to the Man of Tomorrow?", where he would meet his end.
Post-Crisis, Elastic Lad was considered much too silly a concept, but that doesn't mean they couldn't do a tribute to it. In Adventures of Superman #458, Jimmy is infected with a DNA-bending virus (oh Cadmus!) that makes him painfully stretchy.
The aerobics leotard is just a coincidence, we swear! To make sure fans of the more realistic Superman mythos don't freak out, we're told Jimmy couldn't stand this much pain ever again and wants to be cured forever. We shouldn't worry. Or hope.
Type: Transformation
By the Bronze Age, Jimmy wasn't turning into Elastic Lad quite so often, though it could be fun for nostalgia's sake. Jimmy would in fact become Elastic Lad for the last time in the last pre-Crisis Superman story, "Whatever Happened to the Man of Tomorrow?", where he would meet his end.
Comments
... I -- I mean, that's what I imagine the fantasies would be about. For somebody who had them!