adjective

relentlessly severe, stern, or gloomy in manner or appearance.

a hard, dour, humourless fanatic

stern,unsmiling,unfriendly,frowning,poker-faced,severe,forbidding,morose,sour,gruff,surly,uncommunicative,grim,gloomy,dismal,sullen,sombre,grave,sober,serious,solemn,austere,mean-looking,stony,unsympathetic,disapproving