- "Well, business is all very fine. But always remember, you can trust no one. No one but your mother."
- —Gertrud Kapelput to Oswald Cobblepot[src]
In her earlier life, Gertrud worked as a cook for Elijah Van Dahl's parents where they had a secret love. Elijah's parents forbade this relationship between their son and one of their servants. Despite Elijah standing up to his parents, Gertrud was already gone and withheld knowledge she was pregnant with Elijah's child. Some time after this, Gertrud gave birth to Oswald Cobblepot and claimed that his father was dead.
Life with Oswald
Gertrud is presented with a broach from Oswald, and she inadvertently gives him advice on how to take down Fish Mooney.
Whilst at the club Gertrud gets chatted to by mob boss Salvatore Maroni, who has a grudge against Oswald after he had betrayed him. Maroni reveals some home truths to Gertrud that her son is a cold-blooded psychopath, causing her to breakdown, and angering Oswald, who swears to Maroni he will pay. Later back at her apartment, Gertrud asks Oswald not to make a fool of her, and if what Maroni said was true. Oswald continued to deny it, but Gertrud sees right through his lies and leaves the room.
With the help of Butch Gilzean, Oswald finds her inside her cage at a warehouse and attempts to bust her out with bolt cutters. However, Theo and Tabitha Galavan are waiting for them and the gate is only accessible with a certain key. In the end, Gertrud is let out and Tabitha throws a knife in her back. Before succumbing to her wounds, Gertrud states that she is now aware of her son's activities, but still considers him a good boy. As revenge, Cobblepot slashes Theo's throat before escaping through a window.
- "My beloved mother always believed in me. Even when I doubted myself, she held firm."
- —Oswald Cobblepot[src]
Oswald avenged her death by capturing and brutally beating Theo with a bat. Theo was subsequently executed by Jim Gordon. After Theo was resurrected from the dead and became Azrael, Oswald had him killed again, with Butch helping him to carry out the deed.
Despite Tabitha Galavan being the one to actually murder Gertrud, Oswald decided to bide his time when it came to getting his revenge on her, which gave the impression to others he decided to spare her. Knowing about Tabitha's love for Butch, a bond which grew over the years, Oswald helped in curing Butch of his condition before he coldly executed him in front of Tabitha, which caused her great emotional pain, similar to how Oswald felt when she killed his mother. After murdering Butch, Oswald revealed he lived with his pain for years and would hold off from immediately killing Tabitha, as he wanted her to live with her loss like he did before he finished her off for good.
Eighty seven days later after Gotham descends to become a "No Man's Land" thanks to the actions of Jeremiah Valeska and The League of Shadows, Tabitha still hungered for vengeance for Butch's death. When she attempted to shoot at Oswald, the gun misfired and gave Oswald an opening to finally kill his mother's killer and stabbed her in the heart, also avenging Gertrud.
After Tabitha's death, Oswald had a singing group at his office called the Gertrud Kapelput Memorial Choir, presumably formed under the pretense of honoring his mother's memory while actually serving to stroke his ego. Later Oswald appoints a musical chorus with his name, directed by Arthur Penn 
A few weeks later, Oswald considered naming the submarine Edward Nygma was building for his mother.
As he emerged from Blackgate Penitentiary, having been release after ten years, Oswald claimed to the press that his first action after leaving prison was to lay flowers on his mother's grave. This however seemed to be false, as his focus was more predicated upon getting revenge on Jim Gordon. 
- "My mother was a saint! The only person who truly cared about me. And now she's gone. And I have nothing left!"
- —Oswald Cobblepot to Edward Nygma[src]
The most defining trait of Gertrud's personality is her deep love for her son, Oswald Cobblepot, who loved her in return and was devastated at her death. Gertrud seems to see only splendour and perfection around her, hardly ever harsh reality.
- In the DC comics, Oswald Cobblepot's mother is named Miranda Cobblepot.
- In A Dark Knight: The Blade's Path, it's revealed that Gertrud was Hungarian.