I was not wrong. The humans were foolish and I was forced to bring Judgement on them. And yet because of you...I failed. You must understand the weight of your crime. You must pay for the price for what you've done.
~ MB to Madeline and Samus.
MB (also known as Melissa Bergman) is the main antagonist of Metroid: Other M. She is more or less based on Mother Brain.
She was voiced by Shizuka Itō in the Japanese version, and by Sarah Naid in the English version.
MB was introduced when she saw Samus seeing Maurice's corpse. When Samus saw her, MB was frightened and runs away. She was seen once again and was frightened again, but Samus tried to convince her. Then, MB and Samus were attacked by a soldier using a RB176 Ferrocrusher, but were separated too soon.
Later, Samus meets her again, but MB runs away again. Once again, Samus convinces her that she means no harm. MB opens the door and calls herself "Madeline Bergman". The two had a long conversation about Sector Zero and its Metroids. Samus was still curious about this.
At Room MW, Samus finds another survivor, who is the "true" Madeline Bergman. Samus was shocked and confused and tells Madeline she already met someone with that name. After Madeline shows her ID, she tells Samus that the person she met earlier was actually MB herself, and the two talk about MB's story. Suddenly, MB appears and Samus was about to shoot her, until Madeline stops Samus and walks to MB, despite Samus telling her to step back. Madeline tries to convince MB, but MB refuses all of Madeline's words. Then, she was frozen by one of the soldiers with a freeze gun. MB managed to get unfrozen and sends all the monsters she planned to send in her story. However, after Samus kills all the monsters, the soldiers shoot at MB, and she was killed.
In other media
Super Smash Bros.
In Super Smash Bros. For Wii U, MB appears as a unlockable trophy.
MB is a young woman with blonde hair with a pin Madeline gave to her in her past on the left side and blue eyes.
As Madeline suggests, MB originally didn't have a human form. But when the scientists began creating Metroids, she was given a human form to help create a maternal connection to the creatures.
Before the android MB was created, an artificial brain version of MB existed which was used to control cloned Space Pirates until it was eventually destroyed by Adam Malkovich when it too went rogue.
Her nickname "Melissa Bergman" was given by Madeline herself, to help make her feel more human.