Various digital characters, which are automatic and intelligent, are attempted with the introduction of artificial intelligence or artificial life. Since a character's behavior is designed by a developer, the style can be static and simple. Even complex patterns designed by a developer cannot satisfy various users and easily make them feel tedious. A game should maintain various and complex character's behaviors, but it is not easy for the developer to design them. In this paper, we adopt genetic algorithm to produce various and excellent behavior-styles for characters especially focusing on Robocode which is one of promising simulators for artificial intelligence.