iceman
n. countable C1 Advanced US //ˈaɪsmæn// UK //ˈaɪsmən// ice·man
n. a person who is very calm and does not show any emotions. You use this to describe someone who stays cool and collected even when things get stressful.
n. a person who remains exceptionally calm and composed, showing no visible signs of emotion or stress. Informal in register; often used in competitive or high-pressure environments.
He is a total iceman who never gets nervous.
During the high-stakes poker tournament, he remained an iceman, never letting his opponents see his reaction to the cards.
The veteran negotiator was known as an iceman for his ability to de-escalate volatile situations without ever raising his voice or showing a hint of frustration.
From ice + -man.