Smith family

The Smith family (スミス家) is an Eldian family that lives within the Walls. It is the family where Commander Erwin Smith hailed from.

History
Mr. Smith was a teacher and had his son as one of his pupils. After Erwin asked his father a question during class, Mr. Smith eventually told his son of a dangerous theory. Official history books being full of contradictions and mysteries, Mr. Smith believed that humanity's memory has been wiped out at some point, which might explain why there is no story or memories of the Walls' construction. This theory cost Mr. Smith his life, but encouraged Erwin to seek out the truth about the world's origins and prove his father's guess was correct.

Later on, Erwin joined the army and then the Survey Corps.

At some point, Erwin came up with the Long-Distance Enemy Scouting Formation as a new tactic for the Survey Corps. At first rejected by his superior, it eventually became the formation used for every expedition once Erwin becomes the Commander.

The Uprising arc
Erwin had a discussion with Commander Pixis where he mentioned the conversation he had with his father as a child that resulted in the death of his father.

Return to Shiganshina arc
While on the verge of death, Erwin would suddenly lash out while hysterically repeating the last question he asked his father. This action would cause Levi to remember the commander's last words before leading the suicide attack against the Beast Titan. Levi would then choose to save Armin Arlert with the Titan injection believing it would finally allow Erwin to rest.