Dietlinde Eckhart

Dietlinde Eckhart (デートリンデ・エッカルト, Dētorinde Ekkaruto) is the main antagonist of the Fullmetal Alchemist movie Conqueror of Shamballa. She is a German-born, soft spoken woman with radical visions for the future of her troubled country.

Background
Little is known about Eckhart's past, making her a rather mysterious character throughout. First introduced as the chairman of the Thule Society by Haushoffer, she is a woman solely driven by her ambitions. Dietlinde seems to have some knowledge of alchemy (which she calls "magic"), and is additionally a staunch believer in a parallel world to her own which she refers to as "Shamballa". Her influential high status within the Thule Society is what eventually brings her to meet Hohenheim of Light, a man who confesses to have great knowledge of alchemy and to be from another world.

In her mind, she believes that harnessing the magical weapons from these far-off lands will be able to help her own, which is in the midst of political upheaval. Her ultimate goal being to help the successful take over of Adolf Hitler and the Nazi Party.

Conqueror of Shamballa
Under Eckhart's command, and Hohenheim's unwilling advice -- now having been kidnapped into service, the Thule Society begins to actively find ways to reach the other side. The first of these becomes the hunt for a powerful dragon from Shamballa which is rumored to be hiding in the country-side. The dragon's magic planned to be used as a catalyst in opening The Gate. After capturing Envy and bringing it back to her headquarters, Dietlinde is able to open The Gate for a brief period long enough to send through a scouting party. Her attempt backfires, however, and the armored scouts are sent back from Shamballa in dead heaps.

In a second attempt, now using Alphonse Heiderich's rocket technology and Hohenheim's direct sacrifice, the Thule Society is able to open The Gate long enough to send Eckhart and a fleet of flying rocket ships through. Crossing over, she undergoes a severe physical mutation which now also allows her to fully use the alchemy she had learned on her own world at will. The Gate children seem to have bonded with the armor she was wearing, but also have had some affect on her mind. Eckhart also seems to have a complete mental breakdown once she reaches Central City, and is determined to completely eradicate all life in Shamballa.

After Edward Elric manages to sneak aboard her ship, the two have a brief confrontation where she confesses she's doing all this because she ultimately fears this power she cannot fully control or understand. She believes that the people in Ed's world must and will attempt to conquer hers, given their alchemic powers and the other weapons she believes they possess. Ed cannot persuade her to surrender voluntarily, and tries to force her instead, until Alphonse, using his special alchemy to control suits of armor steps in and helps his brother defeat Eckhart, who is eventually sent back to her world along with her army.

Once back, Dietlinde Eckhart is shown to have made a more severe transformation which makes her completely unrecognizable. The black miasma of the Gate has covered her entirely, even altering her voice so it is no longer definitively male or female. She insists she wants to be sent back, to be given another opportunity -- her sanity now completely gone. Because she doesn't know that Ed or Al have come through as well, she tries to force Noah to open the Gate, since Noah absorbed Ed's alchemic knowledge previously. The parallel German Maes Hughes quickly draws his gun, shooting down the mad woman and killing her on the spot, despite returning her to her human form.

Trivia

 * Her character seems to be based on an actual historical figure by the name of Dietrich Eckhart, who in many ways is her male counterpart. It is not clear if he was the Leader of the Thule Society, although it is known in Nov. 09, 1923 he helped Adolf Hitler in the Nazi Party's failed Beer Hall Putsch. He died later that year in December in prison of a heart attack.
 * It is possible that she may be the earth equivalent to Dante, as she resembles Dante's original form, cares only for herself and not for the lives of others, and took the form of multiple bodies, as well as using her subordinates as pawns in her scheme. Though she doesn't share Dante's romantic feelings towards Hohenheim, however (in a ironic twist) both have used Envy as a tool to further their master plan.
 * It's unclear if she knows about homunculi (since 4/7 of them died before the movie, except Envy, Wrath, and Gluttony) it's possible the gate children made her knowledgeable enough for her to be aware of their existence or know that the "Great Serpent" is actually the homunculus Envy.
 * She is the only character from Earth to acquire alchemy going to the other side, though The Gate Children had something to do with it.