Mister Hammer, also referred as Mister Abramovici, was born a conjoined twin with his brother Sickle in Siberia, Russia. When their father went to work one day, he was informed that his wife had gone into labor. He rushed home, only to find that his wife had died due to complications and that their twins were connected at the shoulder. Furious that his wife had died, the twins' father took them as infants to a bridge where he contimplated dropping them in the water below. He could not bring himself to do it and instead put them in a travelling circus to grow up.
Many years later, Hammer and Sickle were the circus' best act. When the Joker saw the power of the brothers, he instantly wanted them for his crew. Harley Quinn talked to the owner but he refused to give up his best act to the Clown Prince of Crime. The circus owner "mysteriously" vanished soon after.
Joker, now in possession of both twins, needed to find a way to disconnect the two. With the creation of Arkham City, Joker did not have many options operating out of a super prison. The clown eventually hired master surgeon Thomas Elliot who successfully separates the two. Joker rewarded the man with a suitcase of jewels.
Not wanting to have two one-armed henchmen, Joker chose Hammer because, like the clown himself, he was right handed as well. Joker ordered Harley to kill Sickle by throwing him into the river.
Although never specified in story, Mister Hammer somehow escaped Arkham City with Black Mask. Whether his escape was allowed by the Joker or not was never mentioned.
Loose in Gotham City, Robin was sent to recapture the two criminals. He was successful and Black Mask and Mister Hammer were successfully returned. When Mister Hammer came back to the prison, he rejoined the Joker in Joker's Funland.
When Batman goes in Joker's Funland and tries to find Joker, who remotely tried to assassinate Catwoman, he goes in the vents and tries to surprise the Joker, but he comes into the middle of Harley's announcement. She explains to her group that Doctor Stacy Baker failed Joker and that she could not cure him. Baker pleads that she could not do anything, but Harley calls her a quack, and then kicks her from Joker's office onto the floor below. Harley announces "Do you want to see a show?" and they start to chant "Kill," as Mister Hammer tries to kill her with his sledgehammer, but she starts to crawl away. As soon as Mister Hammer got her cornered, Harley stops him by saying that the Joker needs her alive, so she can get tortured more. The thugs dragged her away, as Batman follows them, going through a bunch of thugs.
After saving Stacy Baker and getting the Remote Electric Charge, he makes his way to Joker's office, where Harley locks the doors to keep him from getting in. Yet, by using the REC, he knocks the steel doors, blocking him from the Joker. Harley yells at him for knocking the steel doors, but as soon as he grapples up to the office, Mister Hammer kicks back down to the floor. Harley says, "Meet Mister Hammer. He was going to teach you some manners." After fighting Mister Hammer and a bunch of thugs, he wins and makes his way towards Joker, yet he finds him dead and Harley crying. However, it was just a gag and Harley knocks out the Bat, with her bat.
Mister Hammer later again fought Batman alongside with a TITAN Henchman and Joker's thugs, and was ultimately sounded defeated by the Dark Knight.
After the Joker's death, Mister Hammer was reunited with Sickle at the Steel Mill, talking about how they wanted to be together again, going as far as to consider getting their bodies stitched together so they would once more be conjoined.
- Mister Hammer was voiced by Fred Tatasciore.
- Mister Hammer has a Hammer and Sickle "☭" tattoo, a symbol formerly used by his country, Russia whilst part of the Soviet Union. It is also fitting for him and his brother, due to their names and weapons respectively. 
- 9 Appearances of Mister Hammer (Arkhamverse)
- 2 Images featuring Mister Hammer (Arkhamverse)
- Quotations by or about Mister Hammer (Arkhamverse)
- Character Gallery: Mister Hammer (Arkhamverse)
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