Heathcliff Erbe is an anime-only character introduced in the Bonus Episode: Yet Another Man's Battlefield.
He was as an Ishvalan cadet around the same time that Roy Mustang and Maes Hughes also enlisted in the military. Heathcliff joined in hope of becoming an officer and eliminating discrimination from within in the military, much like the motivations of Major Miles, another Ishvalan soldier.
Heathcliff is a man of few words, but he retains a penetrating expression on his face. With it, he was capable of intimidating almost everyone in the academy. He is also determined and dreamy, putting priority in the defense of its land and culture. Due to his race, many other soldiers constantly harassed and threatened Heathcliff whenever running into him, usually exclaiming, "Ew, I've got the stench of an Ishvalan on me!". Humbled by such statements, the young Ishvalan would only lower himself and remain silent.
Around 1903, Roy Mustang first met up with him during one of these encounters, and, disgusted by the fellow soldier's behavior, tried to assist him. He later got into a brawl with the same four men upon seeing the situation yet again and, with the aid of Hughes, finally set everything straight. The three young cadets formed a friendship afterward in their early academy days, up until the Ishval Civil War.
The Civil War
Judging from his Ishvalan attire during the war, Heathcliff had apparently left the military by 1908 - likely due to the government purging of Ishvalan-born soldiers at the start of the Ishval Extermination Campaign. Either way, he met up with Roy Mustang yet again when Mustang was ordered to take out another group of Ishvalans. The reunion was a heavy one, with Mustang in awe over finding his old friend standing before him, and Heathcliff in shock over seeing the man who defended him all those years ago now slaughtering his people. Full of anger and hatred, Heathcliff suddenly fired upon Mustang with a handgun, dropping him, but Maes leaped out in that same moment, immediately retaliating by shooting Heathcliff in the temple, killing him.
Mustang survived due to his State Alchemist watch catching the bullet, but was left in despair over the actions of the military and himself.
- The anime version has Mustang regretting his actions due to the murder of Heathcliff Erbe, whereas in the manga it simply starts there with no previous backstory.