Tien Shinhan is an Earthling who is also a descendant of the triclops alien race, allowing him to possess non-human characteristics and abilities, the most prominent of which is third eye.
When he first met Goku, he was initially hostile towards him, highly due to the influence of his Masters Shen and Mercenary Tao, the latter being defeated by Goku in a battle.
Later on though, he realizes that his masters are teaching too much brutality, so Tien Shinhan decided to just train by himself.
In the end, Tien Shinhan joins forces with Goku and the rest of the Z Fighters against significant enemies.