Online games are a popular form of computer communication, and their continued use is fueled by on online gamer loyalty, i.e., the intention to repeatedly play a game. However, the relevant literature has not sufficiently examined what personality traits should influence users to be loyal and the underlying mechanism, indicating a research gap. Therefore, the purpose of this study is to examine how temperament and character impact online gamer loyalty. Personality and flow theories were used for developing the theoretical model and responses from 1861 online gamers were analyzed using structural equation modeling. The analytical results indicate that online gamers’ persistence, novelty seeking, and reward dependence encourage their loyalty through increased skill, challenge, and flow. Cooperativeness also improves loyalty through increased interdependence, while self-transcendence increases it through increased telepresence and flow. This study is the first examining the impact of gamer temperament and character dimensions on loyalty.