Bo' Rai Cho is a corpulent and jovial native of Outworld who has trained many great warriors, including Liu Kang. Since he is originally from Outworld, he never enters the Mortal Kombat tournament as it would have meant competing on the behalf of Outworld and thus the brutal emperor Shao Kahn. Upon hearing that Liu Kang has been murdered by the Deadly Alliance, he takes Kung Lao under his wing. While a group of Earthrealm warriors prepares for a frontal assault on the Deadly Alliance, Bo' Rai Cho secretly enters the palace and escapes with the body of Li Mei. He regroups with the other Earthrealm warriors led by Raiden and retreats to safety rather than joining the attack. His back story is that he has trained warriors for centuries to compete in the tournaments. After many failures, success finally came when he trained Liu Kang, who defeated Shang Tsung and became champion of the Earthrealm tournament. He appears in Shang Tsung's MK9 ending as having trained Shang Tsung for the role of Outworld's new protector against the now-corrupt god Liu Kang, and makes a brief appearance in the story mode and comic book prequel of MKX. In the story mode he is seen conversing with Raiden about Liu Kang and Kung Lao's deaths before he is nearly killed by Shinnok. Whether he survived the attack is unknown. Bo' Rai Cho was added as a playable character to Mortal Kombat X via downloadable content as part of "Kombat Pack 2".
Source: Wikipedia, "[en.wikipedia.org/wiki/List_of_Mortal_Kombat_characters%23Bo%27_Rai_Cho List of Mortal Kombat characters]", available under the CC-BY-SA License.