Answer
Cyanide was the poison of choice for Richard Kuklinski, a notorious hitman also known as the "Iceman." He favored its discreet nature, as it allowed him to eliminate his targets without leaving any obvious signs of foul play. Mixing the poison into alcoholic beverages or food items, Kuklinski exploited his victims' trust to covertly administer cyanide, earning him a reputation for executing meticulously planned assassinations.