Topper is a character from the Rankin/Bass Christmas television special Santa Claus is Comin' to Town.
He was trying to find his way to the South Pole when he ran into Kris Kringle as he made his way across the Mountain of the Whispering Wind to reach Sombertown. Offering to help Topper out after figuring out why he was traveling through the area, Kris allows him to join him on his journey, narrowly avoiding an encounter with the Winter Warlock when he discovers them trespassing on his mountain.
However, after visiting Sombertown, befriending the new school teacher Miss Jessica, delivering toys to the children, and then escaping the forces of Burgermeister Meisterburger, Topper and Kris are captured by the Warlock via his magical trees, only for Kris to appeal to the Warlock's kinder nature and offer him a toy in return for safe passage back to Rainbow River Valley.
From there, Topper joins Kris in his repeated visits to Sombertown to deliver toys to the kids, despite the Burgermeister's repeated efforts to stop him, including suggesting Kris use the chimney to get into the houses when the doors were locked by orders from the Burgermeister. However, during one visit to Sombertown, Kris falls into a trap set by the Burgermeister using Topper, who had been captured, as leverage to get Kris to surrender willingly to him. Topper is locked up with Kris, the Kringles, and Winter, but thanks to Jessica and some of the reindeer Kris had befriended after they ate some of Winter's Magic Feed Corn, Topper is able to escape with the others. With their home on the Mountain of the Whispering Wind destroyed by the Bugermeister's troops, they are forced to stay on the run until reaching the North Pole, where they set up their new home and workshop, while the Burgermeister and his descendants soon die off, leaving Sombertown a much better place when Santa makes his annual Christmas deliveries there.
Topper apparently keeps in contact with Santa, as he is seen joining SD Kluger with delivering the mail to Santa alongside Winter and several animal friends.
Frosty's Winter Wonderland
Nestor, the Long–Eared Christmas Donkey
The Life and Adventures of Santa Claus