The four temperaments
The idea goes back to Hippocrates and Galen, who linked personality to four bodily 'humors'. That medical explanation was abandoned long ago, but the descriptions survived: the sociable sanguine, the determined choleric, the deep melancholic and the calm phlegmatic.
In the 20th century, psychologist Hans Eysenck related them to two modern dimensions: extraversion and emotional stability. Today research uses models such as the Big Five, but temperaments remain a fun and intuitive way to reflect on yourself.