Rohan Kishibe is a famous mangaka and Stand user to Heaven's Door. The success he's earned at such a young age and his Stand's powerful ability leads him to be very self-important and a total jerk. He and Josuke Higashikata hate each other for a mixture of valid and petty reasons.
Rohan sounds stuck up and has a great deal of smugness to his voice.
In early appearances, he is possessed, so try to sound menacing.