Stoic

A stoic is a person that retains an emotionless expression throughout their daily living, hardly reacting to anything other than with mild boredom, detached interest, dull surprise, or dignified disdain.

Empath: The Luckiest Smurf stories
Empath in his early years as well as the Psyches in the EMPATH: The Luckiest Smurf story series are generally stoics, since they are not permitted to express any kind of strong emotion by the will of the Psyche Master and psychelium dulls their ability to express any emotion. Over time Empath learned how to express emotions to the point where he feels comfortable with himself, while Polaris continually strives to remain emotionally detached in his daily living when he started to live among the Smurfs.