The chief chemist associated with General Ludendorff who specializes in chemistry and poisons. On her role, Anaya said, "Well, it was a small role in this big ensemble, but it is an important character in the story. I'm going to be a big nightmare" for Wonder Woman and Steve Trevor. Describing her character, Anaya said, "Dr. Maru loves rage and enjoys people's pain. She's creating terrible weapons, and her purpose in life is to kill as many people as possible, and provoke as much pain as possible". She researched World War I and Fritz Haber, the scientist who created mustard gas, to prepare for the role. On the character's facial scars, Anaya stated, "I went to Patty Jenkins and asked, 'What happened to her?' And she said, 'She did it on purpose.' I was like, 'What? Patty, you're going further than I ever imagined.' She said, 'She wants to provoke painful suffering, so she tested her own gas on her own face. She wanted to know how deep this form of her gas would go, so she put it on her own face.' You can see half of her face is completely gone. This is the sadistic side of Dr. Maru". She also stated her character "is quite the opposite to the lead role of this movie, one of the strongest characters ever of DC comics, Wonder Woman. I can tell you that Doctor Poison is someone with a capacity to provoke so much pain." On Dr. Maru's relationship with General Ludendorff, Anaya said, "I think that they have a relationship based on loyalty. Ludendorff is a very tormented General that lacks self-confidence. That's why, in part, he takes these drugs that Dr. Poison gives him. They are from different worlds, but they complement each other".
Ares told Diana that he had been imprisoned by the other Gods of Olympus and bound in chains that were secured by Aphrodite through the power of her love. He also told her that years ago, Phobos and Deimos had implanted false memories of Themyscira into her mind, and these had caused her to imagine aspects of her past that had never happened in reality. Meanwhile, Phobos and Deimos entered Themyscira and battled with the Amazons. Diana knew what she had to do, and called Ares to unite her with Phobos and Deimos. He teleported them to her, and using her Lasso of Truth, Wonder Woman bound them through the power of her unconditional love for them, as Aphrodite had done to Ares. With the twin gods defeated, Diana attempted to leave Ares' prison along with Veronica and Izzy, however Izzy's essence had been attached to the realm and could not return to Earth. Izzy was forced to either live out the rest of her days in the prison or live in Themyscira as an Amazon for eternity. She chose the latter and Veronica said goodbye to her daughter. Diana was briefly reunited with her mother, for the first time since she left the island.