Olivier Milla Armstrong (オリヴィエ・ミラ・アームストロング) is the older sister of Alex Louis Armstrong. She is charged with leading Briggs' Fortress, and protecting the country from the neighboring country of Drachma. Unlike her brother, who is cheerful and kindly to all around him, Olivier distrusts everyone when she first meets them, and has no patience for formalities or idle conversation.
She is also, similarly, a firm believer in survival of the fittest. This has earned Olivier a reputation within the military, and in Drachma, as one who should not be crossed, though her subordinates hold her in high regard. Because she readily joins them in hostile situations and disregards the orders of superiors if she disagrees, her subordinates will answer only to her.
[Edit]She always carries a sword at her side, and is proficient enough to be able to defeat her brother with it
as shown in chp.65 / ep.33.
Olivier crosses paths with the Elric brothers when they arrive at Briggs' Fortress. After Sloth infiltrates Briggs, she is able to convince them to tell her about the homunculi that control the military. To help the Elric brothers combat the corrupt higher ups, Olivier goes to Central to work her way into King Bradley's inner circle. Once she learns of plans to create an army of immortal super soldiers, Olivier fights against the homunculi. Although she has no direct control of Briggs, her subordinates still operate it under her wishes, eventually sneaking into Central to help Olivier take control of the government.
Her most loyal soldiers include Miles (マイルズ), who is a quarter Ishbalan, remaining in the military with the hope to someday change the country's perception of Ishbal; and Buccaneer (バッカニア), a large, heavyset man who has been shown with two different pieces of automail in the series.