Individuals who have grandiose delusions strongly believe they are famous, genius, rich and possess super powers. It is a symptom of psychiatric illnesses like bipolar disorder and schizophrenia.
People with grandiose delusions can often continue to socialise and function normally, apart from the subject of their delusion, and generally do not behave in an obviously odd or strange manner unlike people with other psychiatric disorders (who also might have delusions as a symptom of their disorder).
Delusional disorders most often occur in middle to late life and are slightly more common in women than in men. In some cases, it may serve as a functional purpose such as helping a person cope with severely damaged self-esteem and/or depressive feelings.