Mark Wilmans (マーク・ウィルメンス, Māku Wirumensu) is a boy who commits a series of murders in New York in August 1932. Known to the media as the serial killer Ice Pick Thompson (アイスピック・トンプソン, Aisupikku Tonpuson), Mark ends up relinquishing his identity as Ice Pick Thompson to Raz Smith.
He now studies under Smith as his apprentice, and refers to him as Master.
Paula considered having her son drink from a bottle of the elixir she kept, but decided to bury it at her husband's grave instead, with Mark accompanying her. Knowing the kinds of things Szilard's men would do to have the elixir, she told her son to reveal the location of the bottle if someone ever came looking for it.
Mark was occasionally looked after by Lisha Darken, a prostitute and a friend of his mother's.
In November 1930, after Szilard's death and the fire that destroyed most of the bottles of elixir, a group of Szilard's men kidnapped and tortured Paula. Her corpse was dumped into the Hudson River.
Paula had hidden her son in a closet when the men first came to their apartment. Mark stayed there for two days before he was found by police. He identified his mother's body, which was covered in wounds created by an ice pick. Lester, one of the men involved in Paula's murder, wrote in a newspaper article that her death was suspected to be related to a drug crime.
Mark was left with a large amount of money after his mother's death, some of which he lent to Lisha. Lisha told Mark the truth about his mother's death in exchange for money he was withholding because he knew she was buying drugs.
In August 1932, Mark becomes the serial killer Ice Pick Thompson, a moniker coined by Carl Digness because he stabs his victims with an ice pick to the point where it looks like they were shot by a Thompson submachine gun. Mark is seeking to avenge his mother by killing the men who tortured and murdered her.While Mark is targeting Lester, he mistakenly attacks Elmer C. Albatross because they are dressed the same way, and their features and build are similar. Mark realizes his mistake and runs away, horrified at the thought of having stabbed an innocent person. Elmer finds Mark standing on the edge of the Brooklyn Bridge, though Mark does not recognize Elmer as the man he had stabbed earlier. Elmer tells Mark that he will not try to stop him from committing suicide if that's what will make him happy. Mark explains that this is not the case, though he still doesn't want Elmer to interfere. Elmer decides that the best thing to do is to demonstrate how a fall from such a height would be a painful way to die, and reveals his immortality to Mark in the process.
His interest in the immortals and Szilard Quates renewed, Mark visits a bookstore that next day. He strikes up a conversation with the bookstore owner, both having known each other for many years. The bookstore owner notices that Mark looks troubled and asks him what's wrong. As soon as Mark begins referring to the existence of immortals, the bookstore owner warns Mark not to tell anyone else whatever it was that he saw. Mark realizes that the bookstore owner knows something, but leaves after he only receives more warnings. He meets Elmer again on the street, as the latter had noticed the bookstore owner's loud lecturing from outside. Mark flees in terror.
As Mark is running, he chooses to go down an alley and bumps into Graham Specter's gang along the way. Elmer follows shortly afterwards, and asks Graham and his gang to help him look for Mark.
Mark returns to the bookstore that evening, asking the owner again to tell him about the immortals--mentioning this time that one of them won't stop following him around. The bookstore owner finally relents and tells him that he had witnessed Luck Gandor dying and coming back to life earlier that year.
Against the bookstore owner's warnings, Mark visits the Gandor Family's headquarters, the jazz hall 'Coraggioso', where he is invited inside by Tick Jefferson. Mark also meets Maria Barcelito and witnesses the pair's eccentricity first hand. When Mark brings up the topic of immortals in their discussion, Tick warns him, saying the mood around them is especially bad since all of Ice Pick Thompson's victims were members of the Gandor Family. At that moment, Carl Digness briefly enters Coraggioso on the basis of his research on the Ice Pick Thompson case, before he is dismissed due to the Gandor brothers' absence. Tick tells Mark that he can find the answers he's looking for from Carl and the organization he works for (the Daily Days). Mark follows after Carl, deciding he can sell the secret of his identity as Ice Pick Thompson in exchange for the truth about the immortals.
Around this time, Lester hires Raz Smith to kill Mark.
Once Carl notices he is being followed, Mark approaches him and asks about the immortals and Szilard's current whereabouts. As payment, he pulls out his ice pick from his sleeve and reveals that he is Ice Pick Thompson. However, once Carl is able to confirm Mark's identity and motives, he refuses to give him any information beyond the fact that Szilard is no longer in New York. Carl argues that anyone could become a serial killer and give away their identity in exchange for valuable information, running the Daily Days out of business. Mark eventually accepts this explanation and goes home.
Smith, who has been waiting inside Mark's apartment, locks the door once Mark returns. Smith points a rifle at Mark's head and tells him that he is an assassin hired to kill Ice Pick Thompson. However, Smith tells Mark he wants to know why he had become a serial killer before he kills him. Mark repeats the story behind his mother's death. Smith then asks for Mark's last words, and Mark confesses that he mistook his last victim and killed an innocent person instead. However, when Smith shows Mark an article supposedly about the person he stabbed by accident, Mark discovers that Lisha had been killed the day before in a manner similar to his previous targets, and is the one being identified as Ice Pick Thompson's fifth victim. Smith decides to spare Mark's life--he only asks for Ice Pick Thompson's identity in exchange, owing to his lack of a reputation as an assassin.
Smith leaves and tells Graham, Shaft, and Elmer, just outside of the apartment, that he has killed Mark. Mark waits in his apartment for a little while longer before checking Lester's office, and at last finds his final target at Coraggioso. Mark stabs Lester in the shoulder with his ice pick, and Lester, in his confusion and rage, takes a gun from one of the Gandor men and fires at Mark. Elmer suddenly appears and takes the bullet for him--Elmer had known Smith was lying about killing Mark, and had come to Coraggioso on Shaft's advice. After his wounds heal, he explains how Mark had mistaken him for Lester the other day, and that Mark had never killed an innocent person after all. Once Elmer's immortality registers in Lester's mind, he begs him for the elixir. This prompts Mark to take out the bottle of elixir he had brought in a paper bag--the same bottle that his mother had died over. Lester pleads for the bottle, and Mark explains that he had only brought it to destroy it in his face. Lester lunges at him, and Mark takes the opportunity to stab him several more times. Lester manages to take the bottle away from him anyway and drinks the elixir, unwittingly making all his injuries permanent.
The Gandor men make to detain Elmer and Mark, when Nicola Cassetti appears. Nicola identifies Mark, and stops him from confessing he is Ice Pick Thompson. Once the situation in the room is explained to him, Nicola takes personal responsibility for punishing Lester.
Elmer and Mark are let off the next morning. Elmer assures Mark that after he has achieved revenge, he still has a right to happiness. While Mark is still afraid of Elmer, he thanks him for all that he's done.
At some point during that day, Carl suggests adopting Mark, but Mark refuses, pointing out that he is "dead" in the surface world.
Carl meets Mark again that evening at the speakeasy 'Jane Doe', by which time Mark has become Smith's apprentice. Mark explains that he doesn't really intend on becoming an assassin, but he wants to follow Smith seeing as he has taken on his crimes.
By 1935, Mark and Smith are living at Fred's housing facility. They are among those recruited by the Gandor Family in anticipation of the casino party at Ra's Lance.