a baleful look.
a dour, self-sacrificing life.
a forbidding scowl.
a grim man loving duty more than humanity.
a sinister smile.
forbidding thunderclouds.
his threatening behavior.
his tone became menacing.
ominous rumblings of discontent.
sinister storm clouds.
the situation became ugly.
ugly black clouds.
undoubtedly the grimmest part of him was his iron claw.