Jack Frost is a folklore character who can best be described as the personification of cold weather. Every winter, he is said to fly down across the world and blow his icy breath upon its surface, bringing about the freezing temperatures associated with the season. He is often most associated with the Christmas season, largely due to his mention in the classic Christmas carol "The Christmas Song," which features the famous line "Jack Frost nipping at your nose."
Through the years, Rankin Bass would adapt the character for several of their TV specials, changing his portrayal slightly each time. His first appearance was in the 1976 special Frosty's Winter Wonderland (the sequel to the original Frosty the Snowman), where he was depicted as a villain attempting to steal Frosty's hat due to his jealousy at how much more attention Frosty got from children than he did. By the end of the special, however, he is redeemed, and becomes an ally to Frosty who helps him to extend winter so he can stay with the children for some time longer. This version of Jack would later appear again in Rudolph and Frosty's Christmas in July.
In 1979, Rankin Bass decided to give Jack his own special, in which he is depicted as less antagonistic and more sympathetic. Fed up with doing the same routine year after year for all eternity, Jack longs to become mortal, fall in love, and live a normal life on earth with the people he looked down upon for so many years.