Is explorer a proper noun or common noun?

The noun 'Columbus' is a proper noun, the name of a specific person, the name of a specific place.

A common noun is a general Word for any person, place, or thing.

Examples:

• Christopher Columbus (proper noun)
• explorer, sailor, person (common nouns)

• Columbus, Ohio (proper noun)

• city, capital, place (common nouns)

• The Columbus Dispatch (proper noun)
• newspaper, company, thing (common noun)