Sadness is a character in Inside Out and Inside Out 2. She is the blue Emotion and one of the five Emotions inside the mind of Riley, along with Joy, Fear, Anger, and Disgust.
According to an interview with Phyllis Smith, Sadness is the voice of reason: when Joy has an idea, she’ll try and drag her down. She appears to be depressive and shy most of the time, but there are a few instances where she is seen smiling.