Incognito (noun)

A person who is in disguise or hiding their true identity.

Origin:

From italian incognito "unknown, disguised".

Examples:

1. He was an incognito at the party.
2. She was an incognito in the organization.
3. He was an incognito at the conference.
4. She was an incognito at the school.
5. He was an incognito at the bookstore.