Key

Golden Age

The Key was an originally one-shot JSA villain. He was a major crime syndicate leader with agents across the world. He was being chased by the JSA. So, he ended up jumping out  a cable car and seemly to his death (he hasn't been seen since).

Modern Age

A new and seemly unrelated villain named Key appeared in Justice League of America (vol. 1) # 41. He was a chemist that worked for the villain team Intergang. Later, he used "psycho-chemicals" to allow him use the unused 90% of his brain (the writers still thought humans only use 10% of their brains despite that not being true). This allows him to use 10 senses that uses to commit crimes. He uses a Key-Gun and has henchmen called "Key-Men". He had several clashes with the JLA, but just disappeared. He returns two years later in real time. He was apparently in a coma due to the chemicals, which now changed his appearance (as seen above) and enhanced his mental powers. He broke in the JLA's HQ and trapped the JLA members into various fantasies via "a dream-like flu" he made. However, Conner Hawke (who wasn't there when Key did this) stopped him by beating him up when he was distracted. Key was thrown in the Arkham Asylum, where he unsuccessfully tried to get Batman to kill him (claiming he was trying to "escape life"). In the aftermath of  the storyline "World without a Justice League" (see JLA #120-125), he was sent to the "dream realm" (not to be confused with the Dreaming). He later escaped by unknown means. The  Key was seen in a special prison cell, which negated his powers. He somehow escaped off-panel. In Final Crisis, he was a member of the Secret Society of Super Villains. In The New 52 universe, he started at riot at the Arkham Asylum to distract the Justice League for a then-new villain.

References

http://en.wikipedia.org/wiki/Key_(comics)