Grandpa is an elder Ishvalan who lives in the slums. In the 2003 anime, he is Leo and Rick's grandfather.
Manga and the 2009 anime
He only appears briefly, helping Scar heal from his wounds in his battle against Gluttony and Lust.
2003 anime
Grandpa has a larger role in the 2003 anime, as Rick appears in more often in the anime than he does in the manga. Aside from lodging Scar, he tells Rick and Leo the truth about their mother and her death after their brief disappearance.