
Jack is the main hero of Jack and the Cuckoo Clock Heart. He was born with a frozen heart (literally), so his heart had gotten replaced with a cuckoo clock. Jack had to follow 3 rules: don't touch the hands of the clock, manage his anger and not to have any romantic feelings for anyone.
If not, his clock would break and he would die.
He fell in love with Acacia, a Spanish girl, when he was walking around town one evening. He died at the end of the movie.