Why was he called the man with the iron heart?

He was called "the man with the iron heart" due to his reputation for being ruthless, determined, and emotionally detached in his leadership style. This nickname often refers to Reinhard Heydrich, a high-ranking Nazi official known for his role in orchestrating the Holocaust and his brutal enforcement of Nazi policies. His cold demeanor and unwavering commitment to the regime's ideology earned him this ominous title, symbolizing both his strength and lack of compassion.