|We exploited hatred. We kept feeding our resentment. We even thought our hate would save us... We dumped every problem caused by our shortcomings onto an "island of devils." And the result... was the birth of that monster... which has now come to return our hatred upon our own heads. ...If it's possible... for us to have a future again... I will not make the same mistakes... I swear it. If we see... another tomorrow...|
|— Muller regrets the misdeeds of his nation|
Muller (ミュラー Myurā?) is a secretary (長官 Chōkan?) in the Marleyan military. When the continental mainland of Marley is annihilated by the Rumbling, Secretary Muller rallies Marley's remaining forces to Fort Salta in a desperate final effort to stop the Founding Titan's advance.
Muller is an older man with short light hair styled in an undercut and a thick beard running the length of his lower jaw. He also has noticeably thick eyebrows. He has only been seen wearing the standard Marleyan uniform.
Muller seems to be a rather introspective man, capable of recognizing the faults of Marley. He is able to recognize Marley's hand in radicalizing Eren Yeager into beginning the Rumbling, and makes the claim that he will change his ways if he is given the chance to. However, it has also been shown that he is a rather fearful person, as he orders the airships to begin bombing immediately upon a slight movement of the Attack Titan, despite the airships not yet being at the right altitude, while also being visibly frightened.
After Marley is ravaged by the Rumbling, Muller leads a contingent of Marleyan soldiers in a last-ditch effort to stop Eren Yeager from Fort Salta. As the base's airships deploy to bomb Eren's Founding Titan, Muller reminds his soldiers of the responsibility they hold. However, he also reminds them that Marley's hatred for Eldians is what has brought this attack on their nation and promises to change his ways if he is ever given the chance. The airships begin dropping bombs on Eren, but they are not accurate enough to destroy his nape. To Muller's horror, the airships are all wiped out in one attack from Eren and his Titans.
The arrival of forces from Paradis to engage Eren revitalizes Muller and he orders the remaining soldiers in the fort to deploy cannons to fire at the Colossus Titans with Eren. As the Marleyans begin manning cannons, they see a group of Eldian survivors entering the fort. A standoff begins and Muller arrives with a pistol to confront the Eldians. He fires his pistol into the air to get both sides' attention and convinces them to work together to defend the fort from the Titans. As he helps one of the Eldians up, he asks the man to agree to work with him. The truce is short-lived, however, as a smoke is suddenly released into Fort Salta which causes all the Eldians present to transform into Titans.
After Eren is killed the Eldians all return to their human forms and Muller leads his forces out to meet them. The soldiers hold the Eldians at gunpoint and Muller demands that they prove they are no longer Titans. Mr. Leonhart tries to suggest using a blood test but Muller insists that he and his soldiers need immediate reassurance. Before he can give the order to kill the Eldians, one of them comes forward and points out that if they still had any Titan abilities they would have already used them to fend off the soldiers. Satisfied with the man's argument, Muller orders his soldiers to lower their guns.