suffix
Mr.; Ms.; formal title after a name
A formal, respectful suffix attached to a surname, full name, or sometimes a public figure's name. Common in news, reports, and formal writing; less warm and less conversational than さん.
記者会見で山田氏は新しい計画を発表した。
At the press conference, Mr. Yamada announced a new plan.
スミス
A comment arrived from Ms. Smith.
noun, suffix
Used as a noun or suffix for a historical or genealogical clan or family line, as in 藤原氏 or 徳川氏. This is not the everyday honorific title sense.
平安時代、藤原氏は大きな権力を持っていた。
In the Heian period, the Fujiwara clan held great power.
pronoun
A formal written pronoun-like use referring back to a previously named man or public figure. It sounds journalistic or official rather than conversational.
田中一郎氏が講演した。氏は地域医療の課題を語った。
Mr. Ichiro Tanaka gave a lecture. He spoke about issues in local healthcare.
counter
A formal, respectful counter for named people, usually seen in expressions such as 三氏, meaning 'the three people/gentlemen.' In ordinary conversation, 人 is much more common.
会議には、田中氏、佐藤氏、鈴木氏の三氏が出席した。
Mr. Tanaka, Ms. Sato, and Mr. Suzuki, the three of them, attended the meeting.