“In the first week of December, 1980, [John] Lennon bought an early Christmas present for five-year-old Sean. He was never able to give the present to his son; on December 8, John was murdered. Amid the grief and chaos in the Lennons’ home that followed the unthinkable event, the hidden present – a tiny Akita puppy – was almost forgotten. When Sean was finally given the present his father had left behind, the puppy was thin and weak. Sean named her Merry [after] Merry Christmas.”
source: the liner notes for Working Class Hero: a tribute to John Lennon, a compilation of Lennon songs covered by Red Hot Chili Peppers, Screaming Trees, Blues Traveler, Collective Soul, et al.