This wise man, called only "Master", is a former Warrior Priest of Ishval who mentored the young Warrior who would go on to become the infamous serial alchemist killer Scar.
In the manga and 2003 anime, Scar's Master had a black mustache, making him one of the few fully Ishvalan with a hair color other than white or silver, but in the 2009 anime, his mustache color was changed to match the others of his ethnicity.
His Part in the Story
When the Ishval Civil War came to a close, Scar and his Master were separated and the wise priest took refuge in the South of Amestris with other evacuees, but increasing State Military presence drove him east to avoid confrontation. Hearing the vicious exploits of his former pupil, he appears before Scar in Chapter 26 and warns him that his senseless vengeance will only bring about more senseless vengeance, perpetuating the cycle. He tells the younger man that he understands his hatred for State Alchemists, but that - for the time being - he must endure that hatred and keep it from turning him into a beast, a message that (though he continues on his swath of revenge) Scar remembers multiple times throughout the series and just begin to understand when he found Winry pointing a gun at him, intending to show retalition for her parents' deaths. Scar's Master returns again when Ishvalan refugees are asked to help in the attack on Central City just before The Promised Day.
In the alternately adaptation, Scar's master was one of the few survivors of the covert operation of which Martel was a part, and which triggered the Ishval massacre. He later speaks on behalf of the Ishvalans at a refugee camp when Mustang and his men arrive looking for Scar.
Trivia
Scar's master in 2003 anime.
In chapter 86, Scar's Master says one of the most widely quoted sayings by Mahatma Gandhi : "You must be the change you wish to see in the world".
In that fashion, this would highlight the fact that Ishval can be based in India, since both nations have a lot in common: similar color skins and clothes, great belief in their own religion with their respective religious leader and same old language (Sanskrit).
