Ice man
Iceman or ice man was a colloquial term given to someone who was unusually calm and focused under pressure.

While playing poker, Commander Riker called Lt. Worf "iceman" after winning at least two consecutive hands of the game. ()

The Klingon term for "ice man" was d'akturak. Federation Ambassador Curzon Dax gave this nickname to Koloth at the Korvat colony negotiations, referring to Koloth's "icy" demeanor at those negotiations. ()

External link 
 

Nicknames