Boris Niewald arrived in Winden in 1986, apparently on the run. He encountered Ulrich Nielsen and Katharina beating up Regina Tiedemann and scared them off by brandishing a gun. He gives Regina the name Aleksander, but Hannah Kahnwald later sees him burying a bag in the forest containing the gun and a passport with his photo and the name Boris Niewald issued in Gießen, swapping it for another issued in Marburg for an Alexander Köhler. Dark Season 1 Episode 9: "Everything Is Now"
By 2019, Aleksander is married to Regina and director of the power plant, a position once held by his mother-in-law Claudia. Hannah is his massage therapist.
On June 20, Aleksander's attention is piqued when he comes across the headline, "Murder in Marburg unsolved 33 years later. Search for two fugitive perps still on" while reading the newspaper. He ponders how an investigation can still be ongoing after more than three decades of searching.
Ulrich finds a locked door in the cave that seemingly leads to the nearby nuclear power plant. He tells Charlotte to request a search warrant for the power plant. Aleksander blocks this and when Ulrich requests access he refuses him entry, citing security regulations. He also has things taken away before the police can find them. Dark Season 1 Episode 2: "Lies"
Hannah, having taken Aleksander's bag to their massage appointment, blackmails him with it. She demands no money, only the destruction of Ulrich's life. In turn, Aleksander calls his friend in the Winden Police, Torben Wöller, and tells him to dig up dirt on Ulrich. He also mentions that they will soon be able to return the barrels of waste, which had been stored on a truck. Dark Season 1 Episode 9: "Everything Is Now"
June 24 Edit
Clausen has gone to the nuclear power plant to question Aleksander. He tells him that he denied Ulrich Nielsen entry to the plant due to stricter security after the Fukushima disaster. He says the door to the caves was sealed shut in the 1980s as a security measure, so it would not be possible for someone to enter. Clausen tells him he finds it unusual that everyone who was born in Winden seems to remain there. Aleksander attributes this to the steady employment available at the power plant, although that will change soon. Clausen then points out that Aleksander is an exception, having come from somewhere else, arriving in 1986, around the time that Mads disappeared. Aleksander points out that he arrived several weeks after Mads' disappearance. Clausen then asks why he took his wife's last name, which was unusual at that time. Aleksander says that as Regina was an only child, they had wanted to preserve the name. He asks what his original name was. He tells him Köhler.
June 25 Edit
Aleksander is on the phone asking why Clausen is so interested in the power plant and why is he really there. Regina announces that Bartosz is missing, and his bed was not slept in. Aleksander thinks he must have gotten back together with Martha, but Regina says no one is answering there. She asks Aleksander to tell her everything is okay, which he tells her—unconvincingly.
June 26 Edit
Clausen closes in on Aleksander, stating he is being charged for identity theft and obstruction. He says he is looking for Aleksander Köhler, who is his brother. He says he believes his height is different to what his documents state and curtly states "you are definitely not my brother."
June 27 Edit
Clausen hands Aleksander a search warrant for the Winden Nuclear Power Plant. He vows that even if he cannot prove that Aleksander murdered his brother, he will still get him for whatever is happening in Winden. Aleksander, distraught, begs Torben to help him and stop Clausen, but Torben says it is impossible, and perhaps things will be better now the truth is out.
2019 (alternate reality) Edit
November 5 Edit
Hannah visits Aleksander and says sorry about what happened to Regina. She asks Aleksander how he and Bartosz are doing and tells him she wants to offer him a deal, telling him she has something that was his and wanted to return it. She brings out a bag, and asks him if he remembers it, Seeing Aleksander's worried face, Hannah tells him that the contents of the bag were safe. Aleksander asks if what she wants is money, but she refuses because she wants Charlotte "destroyed" and to lose everything.