A bad-tempered or gloomy person is sullen. Sullen people are down in the dumps.
If someone is dark, dour, glum, moody, morose, or sour, they're also sullen. Teenagers are often described as sullen, especially when they're being grumpy and silent. You often hear about "a sullen silence," which is when someone is quiet, but obviously in a lousy mood. If a sullen person is talking, they're probably not saying much, and they might not be doing much beyond grunting. A sullen person isn't much fun to be around.