Simeon Fleischer was born in Fulda, a city in the German states of the Holy Roman Empire, during the mid-16th century. He trained as a wool weaver, a profession that provided him with some stability and respectability. He moved frequently from one town to another, never staying long enough to establish deep roots. 

Sometime in his adult years, Fleischer began a calculated cycle of exploitation: he targeted women, particularly widows, tradesmen’s daughters, and maids, who could offer him a dowry, inheritance, or personal savings. In Marburg, he married a young virgin whose father’s estate gave him 160 guilders, a considerable sum for the time. After less than five months, he murdered her and sold her clothing for additional profit.

Fleischer’s second marriage, to a 40-year-old widow, lasted only four weeks before he killed her and took 40 guilders. He continued marrying across towns such as Hanau, Frankfurt, Miltenberg, Bad Mergentheim, Würzburg, Dinkelsbühl, Ellwangen, and Schwäbisch Gmünd, always presenting himself as a respectable suitor. In many cases, he married women from respectable working-class families such as carpenters, bakers, tailors, or blacksmiths which allowed him to blend in as a fellow tradesman.

Fleischer was adept at exploiting dowry customs, where brides often brought money, property, or valuable goods into the marriage. He traveled across Franconia, Baden, Württemberg, Alsace, and the Palatinate.

Between approximately 1575 and 1581, Simeon Fleischer allegedly married 31 women across various German territories and murdered 19 of them for financial gain. His method was consistent: marry quickly, extract whatever dowry or wealth he could, then murder the woman and vanish to another town.

The spree began in Marburg, where he married a virgin and secured 160 guilders from her family. Less than five months later, she was dead—murdered by Fleischer, who took her clothing and money. From there, his pattern intensified. He married a 40-year-old widow, then murdered her after four weeks for 40 guilders. In Hanau, Frankfurt, Miltenberg, and Würzburg, he repeated the same cycle: find a bride, wait days or weeks, then kill and rob her.

Victims were often drowned, strangled, stabbed, or thrown into rivers, wells, or latrines. Their bodies were typically abandoned in secluded areas. In Bad Mergentheim, he tricked a carpenter’s daughter into thinking they were returning to her parents, then threw her into the Main River near Würzburg. In Rothenburg ob der Tauber, he killed a tavern owner just eleven days after marrying her. In Schwäbisch Gmünd, a landlady became another casualty.

He moved across towns like Pforzheim, Baden-Baden, Rastatt, Strasbourg, and Haguenau, using new identities and marriage as cover. In Wissembourg, he married a wealthy widow and later murdered her and her daughter in a forest near Kandel. In Landau, he threw a maid into a well after stealing 18 guilders.

The climax came in Neustadt an der Weinstraße, where he married a tailor's maid. Just seven days later, after murdering her, he was caught red-handed at the crime scene. Arrested and tortured, Fleischer confessed to murdering 19 of his 31 wives in a span of just six years. He provided rough locations for many of the killings, including rivers, roadsides, forests, and mills across central Germany.

On January 18, 1581, he was executed by impalement, his body torn with red-hot tongs, his hands and feet severed, over the course of three full days.