1. If you use a person's name or likeness without their permission, you may be violating their right to privacy. This is especially true if you use their name or likeness in a way that could be damaging to their reputation.
2. If you use a person's copyrighted material without their permission, you may be violating their copyright. For example, if you include a copyrighted photograph in your novel without the photographer's permission, you may be liable for copyright infringement.
3. Defamation: Making false statements of fact that are damaging to a person's reputation can constitute defamation. For example, if you write that someone was unfaithful in their marriage, you may be liable for defamation if this is false.
4. You can't use real people's likenesses or identifiable characteristics in works that may place them in a false light or portray them in a false or misleading way.
5. Using a person's name, nickname, or identifiable characteristic in a false advertising endorsement could have legal consequences.
6. If you use a person's name or likeness in a commercial context (e.g., on a product or in an advertisement), you may need to obtain their consent. For example, if you use an image of a celebrity to sell a product, you may need to get their permission to do so.
It is important to note that these are just some of the general rules governing the use of real people in fiction. There may be additional restrictions depending on the specific jurisdiction in which you live or publish. If you are unsure about whether it is legal to use a particular person's name or likeness in your work, it is always best to consult with an attorney.