Monokuma is often described as easygoing and cheerful at first glance, but with very sinister undertone. However, he always rather quickly reveals his evil nature by describing killing games and his desire for despair, and he is very well known for his habit to say and do whatever he wants to. He loves despair, violence and chaos, summarized in one of his catchphrases "thrills, chills, kills!". He also has his own signature laughs, a sadistic "puhuhu" ("upupupu" in the Japanese version) and a mocking "ah-hahahaha".

Voice reference: 

https://www.youtube.com/watch?v=ihz-GgG35N8