Happy Birthday: Doll Man
Darrell Dane was a research chemist working on ways to chemically condense matter. When his fiancee Martha Roberts was kidnapped, Dane downed a formula he had just developed and shrank himself to six inches tall while retaining his full mass and strength.
After rescuing Martha, he decided to continue his miniaturized adventures and donned a costume she created for him to become—Doll Man. Dane later became a member of the Freedom Fighters, a group of superheroes that, after Crisis on Infinite Earths, merged with the All-Star Squadron.
Unfortunately, spending so many years compressed warped Dane’s mind, leaving him mentally unstable. For a time, he was confined to a mental institution—presumably in a very small room.