Rick is a young boy of Ishvalan descent.
In the manga and the 2009 anime
In the manga, Rick lives in the slums on the edge of East City. Though he doesn't look like an Ishvalan at first glance, he has inherited his ancestry and red eyes from his mother. In the 2009 anime however, Rick looks fully Ishvalan with red eyes and white hair. Along with an elder Ishvalan, Rick discovered the unconscious Scar floating in the sewers after the man's fight with Lust and Gluttony underground. He responds positively when Scar asks (apparently numb and unable to move) if his right arm is still intact and appears very impressed by the Dragon's Pulse tattoo.
As a result of his hard life as an Ishvalan, Rick is a shrewd young man, as he reveals that he would have merely robbed Scar of what little he had and thrown the man back into the water had he not been an Ishvalan. Additionally, Rick cares a good deal for Scar, tending to his wounds and feeding him until he regains his strength and scolding the intimidating murderer for working out before his injuries have fully healed.
In the 2003 anime
In the 2003 anime series, Rick is the younger of two Ishvalan orphan brothers living in the slums of Central City. He and his brother Rio befriend Scar and later Alphonse Elric after the young alchemist's doubts about his identity cause him to run from Edward's side. Unlike his older brother, Rick fondly remembers his mother (who had died in the Ishbal War) and spends much of his appearance countering Rio's anger towards her for abandoning them. Rick is kidnapped by a pack of mercenaries hired to search out Ishvalans and rebels, but when Rio, Alphonse, Scar, his grandfather, Edward and Winry come to his rescue, the young boy is struck in the chest by a stray dagger. Fortunately, his mother's keepsake locket protects him from harm and comes apart, revealing the eye medicine contained within, and it is explained to the brothers that their mother had not run away to save herself, as Rio had thought, but was suffering from an eye deficiency and had only run away to find them because she could not see them in front of her. As evidenced in Episode 36, he could have posttraumatic stress disorder as a result of his experiences during the Ishval Civil War.