Donkey

"I've made a lot of saddles in my day. Horse, donkey and now, dragon."

- Gobber in "Viking for Hire"

Donkeys are equines mentioned very briefly in the How to Train Your Dragon Franchise.

Description
Donkeys are domesticated equines (related to horses) that are not depicted in the Franchise, but are mentioned. In real life donkeys (Equus africanus asinus) are the domesticated sub-species of the African wild ass. Humans have been utilizing this animal for greater than five millennia. Donkeys are commonly known for their horse-like appearance, long ears, loud bray, and the perception of a "stubborn" temperament. There are many different breeds of different sizes and colors.

Function
In the Franchise, Gobber's statement at the top of the page implies that the Hooligans, or at least Vikings in general, used donkeys for riding.

In reality, donkeys are used for riding and many other things. They are more often used as a dray animal, hauling loads on their backs or in carts. They are very strong relative to their size. They may also be pets on occasion. Donkeys can be milked and their flesh eaten, though there are varying strong views world-wide about consuming equine meat.

Dragons: Riders of Berk
In the episode, "Viking for Hire", Gobber realizes that his primary job - making weapons - is now largely defunct as they are no longer fighting dragons. Hiccup tries to find another task for him to focus on - making saddles for the dragons. Gobber is an accomplished saddle maker for horses and donkeys, but did not do so well with dragon saddles, as he wanted to put too many accessories on them that did not work with the dragon.

Dragons: Rise of Berk
"Dronkeys", dragon-donkey hybrids from Dreamwork's Shrek Movie Franchise, were released in this game in 2015, and on a limited basis since then.