Captain Cold is said to be a legendary Flash villain but I didn't know who he was at all while I did vaguely know Killer Frost. It seems to me that Killer Frost had more appearances in recent animated DC series than Captain Cold. B/C of that I knew who Killer Frost was but, as I really only read a small handful of DC titles (none of them Flash), I never really knew who Captain Cold was.
I wonder if many other people had the same experience and whether exposure in animated shows such as Justice League played a factor.