He is portrayed by Robin Lord Taylor.
In the second season, Oswald is dethroned as Gotham's crime boss by the antagonist Theo Galavan, who killed Oswald's mother and later set him up for the kidnapping of Mayor Aubrey James. Oswald later teams up with James Gordon, Harvey Bullock, Alfred Pennyworth, Selina Kyle, and several of Penguin's mob associates, in order to lay siege on Galavan's penthouse and prevent him and the Order of St. Dumas from killing Bruce Wayne. After dealing with the Order, Penguin and Gordon kidnap Galavan, and Gordon later executes him by the harbour, in order to prevent Galavan possibly getting away with his criminal acts.
Penguin later takes responsibility for Galavan's murder, and as a result is transferred to Arkham Asylum, and gets subject to torturous "treatments" at the hands of director Hugo Strange. Penguin is later declared sane after his violent tenancies are removed, and he is released back into the public. After being shunted by his mob associates and best friend Edward Nygma, he ends up meeting with his father Elijah for the first time and moves in with him and his family, although Penguin's stepmother and step-siblings don't approve of him. After the stepfamily accidentally kill Elijah in a failed attempt to poison Oswald, his conditioning breaks and he kills and cooks them in revenge for what they did.
After Galavan is resurrected by Strange and becomes the violent warrior known as Azrael, Oswald and Butch Gilzean team up and blow Azrael to pieces with a rocket launcher, preventing him from trying to kill Bruce again.
In season 4, Oswald is again a major crime boss in Gotham and introduces an unofficial law in which criminals are required to carry licenses if they wish to commit crimes, and anyone who disobeys this will be killed. His license system keeps Gotham's criminal underworld in order and keeps the public and police safe for the first time in years, although Gordon doesn't approve of it and turns to Sofia Falcone to try and overthrow Penguin. This leads to Sofia secretly enlisting the help of serial killer and hitman Lazlo Valentin, who then takes on the role as Professor Pyg and plunges Gotham into terror when he begins targeting cops and the homeless. Oswald is later accused of killing a boy he befriended known as Martin, and is sent back to Arkham Asylum.
After escaping Arkham, Oswald later becomes part of Jerome Valeska's "legion of horribles" which has other supervillains as part of the team. Although Oswald hopes Jerome's gang are going to help take back the criminal underworld, he is shocked to find out they would rather plunge Gotham into a state of anarchy and chaos. He defects from Jerome's group and informs Gordon on the legion of horribles plans for the city, which later causes him to be captured and tied up in a blimp carrying Jerome's laughing gas. Before the blimp can be crashed into a crowd of people, Oswald manages to guide it away to safety.
During season 5, Oswald and the other villains begin helping the heroic characters team up against Bane's army in order to protect Gotham City from their sinister agenda. Despite this though, he reverts back to his villainous ways after feeling he wasn't given enough credit for helping save Gotham City, and entered back into a villainous partnership with Edward Nygma/ The Riddler.