There's a reason this thread is named the way it is . . .
First appearance: Batman #121 (February 1959) . . .
. . . but he went by the name of "Mr. Zero" then.
When he appeared again in the 1960s, he had changed his name to "Mr. Freeze", but his real name wasn't as yet known.
from Detective Comics #373 (March 1968)
It wouldn't be until the early 1990s that he would get his tragic back-story and his identity of "Dr. Victor Fries".