The Unicorn was adopted as Scotland’s national animal by King Robert in the late 1300's. The existence of the mythical creature was only disproved in 1825.
The Unicorn was believed to be the natural enemy of the lion - a symbol that the English royals adopted around a hundred years before. According to folklore, the lion and the unicorn hate each other.
Another natural enemy was the elephant. It was always said that the unicorn would always defeat the elephant, despite its smaller size. The Unicorn was believed to have immense strength, and it even couldn’t be beaten by something as large and powerful as an elephant.
Of the stories that are told about the Unicorn there’s one in particular, the water cleansing story which adds to the myth. A snake would come up to the watering hole and poison it, but then the Unicorn would then come along and dip its horn into the watering hole to purify it for all the other animals.
It was said the Unicorn had power to dominate, but instead of using the power for evil, it used it to protect and provide other resources for other animals. In medieval times, when there was this great focus on chivalry, it became the ultimate animal. It could do whatever it wanted because of that power, but it chose to use this power to make better for other things.
When you combine this with all the other stories about its greatness, its power and its ferocity - you can understand why King Robert wanted it as his emblem.