imperturbable

adjective

Unshakably calm and collected: synonym: cool.

Incapable of being perturbed or agitated; unmoved; self-contained; calm.

adjective

Incapable of being disturbed or disconcerted.

adjective

not easily perturbed, upset or excited

adjective

calm and collected, even under pressure

adjective

not easily perturbed or excited or upset; marked by extreme calm and composure