The reason why Liu Kang is a character that has a big part of the games story.
In the story he's the creator of the timeline until the villian of the game ruins it.
But there is much more to his character that I can't fit in text, but to keep it brief
he died came back due to rage he came back but normal, then he destroyed
the other keeper of time the after that happened he became the keeper of time,
made another timeline and that where Mk1 takes place.
LiuKang isn't used often but he is useful so I would say he is Underated