iceman
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.”
“More than 5,000 years after his death, Ötzi the Iceman is still hosting a remarkable mix of ancient and modern microorganisms.”
From ice + -man.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.