Using characters from other novels for commercial or non-commercial purposes without the authorization of the author of the novel may be an copyright violation. This is because the character is usually one of the intellectual property rights of the author of the novel. The author has the right to decide how to use the character and its image. For example, using the character "Harry Potter" as the name of one's own brand or product or service, or using it for advertising or other commercial purposes, could be an offence. Similarly, using a character from another novel as one's own trademark or logo could also constitute an copyright violation. Of course, not all uses would be considered as an copyright violation. If the author of the novel had authorized the use of the novel or if the character used was fictional and would not interfere with the plot and theme of the original novel, the use of the novel could be considered legal. However, if the characters used were real and interfered with the plot and theme of the original novel, or if the appearance, personality, actions, and other characteristics of the characters were similar to the original novel, it might constitute an copyright violation. Therefore, when using characters from other novels for commercial or non-commercial purposes, it is recommended to obtain the authorization of the author of the novel or consult a lawyer to avoid possible legal risks.