Ghilen is a monster which was influenced by Chinese culture. Like many other creatures that have origins in China, the male and female at one point had different names:  the males were known as "Ghi" and the females were known as "Len". It is more widely understood to refer to them by the single term of "Ghilen". In Chinese legends, the creature is said to have the head of a dragon with a single antler, the body of a deer covered with scales, a tail of an ox, and horse-like hooves. The creature was a result of combination of 5 primary elements; earth, water, fire, wood, and metal. Some say a Ghilen can live up to several thousand years.

In the traditional legends, only the male of the species is gifted with a horn, which is usually one but may be several. 
  
It's also a representation of good omen as it is one of the four magnificent/sacred Chinese creatures. The other three creatures are Hongsa (Heavenly Bird), Dragon, and Turtle.
  
In other countries such as Japan or korea, there are also legends about this creature. In Japan the creature is called "Kirin". According to www.pantheon.org, a Kirin or Ghilen is a Japanese unicorn. It's regarded as an animal-god who punishes the wicked with its single horn. It protects the just and grants them good luck. Seeing a kirin is considered an omen of extreme good luck - if one is a virtuous person.
 
Artistic depiction of Ghilen has been spotted in Thailand since the time of King Rama III. However, Thai artists have several different styles of Ghilen. In Himmpan world, you will generally see a Ghilen depicted as one of the 3 types; Chinese Ghilen, Thai Ghilen, and Winged Ghilen.
 
Read more on different types of Ghilens:
Chinese Ghilen
Thai Ghilen
Winged Ghilen