Cryopreservation was stumbled upon by two scientists from England in 1949.
Audrey Smith and Charles Polge were putting a few drops of glycerin into a petri dish containing chicken sperm in order to try and slow down the sperm. The two scientists wanted to study the motility of the sperm, however they found out that adding glycerin had interesting effects. When the scientists accidentally froze these sperm in liquid nitrogen, they survived. As described in Nature, it was the first time in history scientists had successfully cryopreserved living mammalian cells or tissue.