Final Answer:
A client with a diagnosis of delusions of grandeur believes that he is highly important or famous.
Step-by-step explanation:
Delusions of grandeur involve false and exaggerated beliefs about one's own significance, importance, or fame. Individuals experiencing delusions of grandeur may believe they have exceptional talents, qualities, or connections that elevate them to a status of great importance. This contrasts with other types of delusions, such as persecutory delusions (feeling targeted or harassed), referential delusions (believing events are directly related to oneself), or delusions of guilt or responsibility for evil in the world. Therefore, option 1, "highly important or famous," accurately describes the characteristic belief associated with delusions of grandeur.