Erwin Smith

Irvin Smith, sometimes known as Chief Elvin, is the commander of the Scouting Legion. Far-thinking, intelligent, respected, Irvin is an able commander and while he cares as deeply for his men as Rivaille, he would not hesitate to sacrifice them for the future of mankind. He developed the "Formation for Long Distance Enemy Dectection."

Personality
Irvin is portrayed as serious and calculating. While he trusts his men, he is the first to realize that there is a spy interfering with the Scouting Legion and arranging for his/her capture. He is an eloquent speaker, able to sway many people, such as the war tribunal held to judge Eren and the trainees choosing recruitment branches to join.

Irvin is very grim. He accepts all news, good or bad, mockery or praise with the same attitude because he knows his objectives and will follow through with them.

He shares this unique stoic quality with men such as Head Administrator Dot Pixis and Generalissimo Dallis Zacklay. As Armin puts it, these men have the ability to send their men to die if it will further the cause of humanity. They will sacrifice their own humanity in order to bring change to a world where those who cannot sacrifice the important things in life will not change anything.

Plot
Irvin is first introduced in Chapter 1 where he took part in the last Scouting expedition before the fall of Wall Maria.

He is later formally introduced when the Scouting Legion is clearing a town inside Wall Maria. They discover Titans are moving north, towards the Trost District of Wall Rosa. Fearing a breach, they head to Trost District and narrowly save a trapped Eren, Armin, and Mikasa after their mission to block the hole is complete.

From there, Irvin does not reappear until Ch. 18 when he explains the upheaval Eren has caused in the politics of humanity. Later, he successfully gets Eren recruited into the Scouting Legion and arranges for his study by Hanji Zoe, a Titan scientist and squad leader.

At the recruitment drive, his speech about the future of humanity convinces most of the top 10 trainees from Eren's unit to join the Scouting Legion.

After the death of the Titan research subjects, Bean and Sonny, he tests everyone in the Scouting Legion by asking them a direct, but confusing question to gauge their reactions. When this turns everyone innocent, he begins planning the next expedition to capture the spy, guessing they have abilities similar to Eren and are intent on sabotaging the expedition.

However the plan fails as the Female-type titan manages to escape but only after inflicting massive casualities on the Scouting Legion party. Irvin is forced to call a retreat back to the Wall's safety.

For the costly failure of this mission, Irvin is blamed for the fiasco and summoned to the imperial capital to explain. However, he trusts Armin's gamble that Annie Leonhardt is the titan and orders her covert capture enroute to the meeting. He briefly explains this to Nile Dawk.

She is eventually apprehended and Irvin goes into an emergency meeting held to sort out the day's events. He is still there when Wall Rosa is breached.