Mr. Arlert

 was the father of Armin Arlert.

Personality
Mr. Arlert appeared to be a very courageous man, willing to risk his own life in order to escape beyond the Walls. The fact that he was able to design a hot air balloon that would carry him and his wife beyond the Walls indicates that he was a remarkably intelligent man.

History
Mr. Smith and his wife were both killed by Military Police Brigade member Djel Sannes for attempting to escape the Walls.