A person who stays calm and shows little emotion in a crisis is an example of someone who would be described as stolid.
Origin of stolidClassical Latin stolidus, firm, slow, stupid: for Indo-European base see still
Origin of stolidLatin stolidus, stupid; see stel- in Indo-European roots.
- sto·lid′i·ty , stol′id·ness
(comparative stolider, superlative stolidest)
From Latin stolidus (“foolish, obtuse, slow").