In the Pirates of the Caribbean franchise, Elizabeth Swan is known for being assertive and standing up for what she believes in. This is evident in her line, "Commodore, I really must protest." She is not afraid to voice her objections and challenge authority when necessary. Jack Sparrow, Tia Dalma, and Davy Jones are also prominent characters in the series, but they do not say this specific line. Therefore, the correct answer is Elizabeth Swan.