unexpressive

1. He is unexpressive in public, but is said to be affable and accessible, with a quick wit and sharp mind.
   他在公共场合以冷静形象示人，但是据说才思敏捷，并且与人和善。

adj

1. deliberately impassive in manner
   1. deadpan humor
   2. his face remained expressionless as the verdict was read

   Synonym:    deadpanexpressionlessimpassivepoker-faced