If you describe someone as stolid, you mean that they do not show much emotion or are not very exciting or interesting. He glanced furtively at the stolid faces of the two detectives. someone who is stolid does not react to situations or seem excited by them when most people would react - used to show disapproval = impassive (stolidus )
having or revealing little emotion or sensibility; not easily aroused or excited; "her impassive remoteness"; "he remained impassive, showing neither interest in nor concern for our plight"- Nordhoff & Hall; "a silent stolid creature who took it all as a matter of course"-Virginia Woolf; "her face showed nothing but stolid indifference"