Imperturbable (adjective)

1. Not capable of being disturbed or upset; calm and composed.
2. Not easily excited or agitated; composed.

Origin:

Mid 17th century: from french, or from latin imperturbabilis, from in- "not" + perturbare "disturb".

Examples:

1. The pilot remained imperturbable during the emergency landing.
2. The witness remained imperturbable throughout the trial.
3. The doctor's imperturbable demeanor helped to put the patient at ease.
4. The child's imperturbable nature helped her to stay calm during the storm.
5. The leader's imperturbable attitude inspired confidence in his followers.