sad and serious
saturnine - sad
In centuries gone by, Saturn was considered to be a gloomy and forbidding planet in appearance, which then yielded the adjective ‘saturnine’ to describe somebody who shares similar traits. Such people tend to be unpleasant, brooding, and bitter, making them difficult to get along with in either a professional or social context. For that reason, the word is typically used to express disapproval.
I’d rather Gary wasn't on the shop floor dealing with customers. He’s a rather sullen, saturnine young man.
That teacher may have an unfriendly and saturnine manner, but she genuinely cares about giving the students a good education.
It can be hard to be around Mary sometimes due to her saturnine disposition. She is always so aggrieved and embittered about things.