Curate, connect, and discover
ya know what's a great trope?
This stern, serious character, sometimes in a small way an antagonist but not The antagonist, is always seen serious and all, always about enforcing law or something.
Then the hero is interrogated by the villain or by a secondary villain and starts making stuff up such as ''oh yeah no that day I couldn't have set fire to your evil lair because I was at my cousin's birthday party'' and the stern character just plays along like ''yup, name's Roman, the cake was strawberry flavored'' when no one asked him anything.
Or when the hero is making stuff up like ''noooo... that is not Professor Ramirez from litterature department, that's... that's... I mean, of course it's not that because obviously I'm not majoring in litterature... er..." and the stern character just extands his arm for a handshake and lies with a straight face ''yeah nice to meet you, I'm professor Davids from the engineering department, your child is a delight to have in class'' and like the stern character is always making MC's life a hell or something because of their own standards/egoism, but if they have the possibility to just... play along with no idea what the consequences will be but they somehow do it anyway.