Ian (イアン) is a member of the Stationary Guard in Trost District.
Ian first appears in Ch. 5 after Trost District is breached by the Colossal Titan. He compliments Mikasa for killing a Titan that was attacking a group of evacuating civilians.
In Ch. 12, a plan is formed for Eren to use his Titan powers to seal the breach with a boulder. Ian is placed in charge of the elite squad assigned to protect Eren on his mission.
When Eren loses control of his Titan form in Ch. 13, Mitabi and Rico advise Ian to abort the mission and retreat. However, Ian orders his soldiers to continue to defend Eren down to the last man, as Eren is their only hope against the Titans.
In Ch. 14, Eren regains his senses due to Armin's intervention, and Ian orders his soldiers to protect him until he reaches the breach even at the cost of their own lives. Ian uses himself as bait to lure Titans away from Eren, sacrificing his life in order to ensure the success of the mission.