The phrase "a certain gentleman" is correct and usable in written English.
It can be used when referring to an unspecified or particular man, often in a formal or literary context.
Example: "A certain gentleman approached me at the event, offering his assistance with the project."
Alternatives: "a particular man" or "an unspecified gentleman".
The other really big one in my career happened when I was working for a certain gentleman, and I used to ask a lot of questions.
A waitress was mystifyingly insistent on carding a certain gentleman whose graying temples lent him a distinguished air (hint: he's not the fruity-beer type).
When Kempton Bunton offered himself to the police in July, he had a statement with him explaining: "(1) My secret has leaked – I wouldn't like a certain gentleman to benefit financially by speaking to the law.
He claimed that he was the best inside left in the north east, except for a certain gentleman by the name of Raich Carter, who kept him out of Sunderland's first team.
By E. B. White The New Yorker, October 1, 1932 P. 11 The purchase of a sports plane, far from curing him of his taste for practical jokes, only added to a certain gentleman's repertory.
Take, for example, a certain manicured gentleman who took her to dinner one night.
Doesn't Richards recall that even labels such as Motown had people writing songs for their artists, just as Lennon and McCartney wrote for others, while Marianne Faithfull had her first hit with As Tears Go By, written by Mick Jagger and a certain young gentleman called Keith Richards.
Semi-gingerbread-style Caribbean cottages line the narrow lanes, including a haunted house built in 1830 -- a certain plump gentleman with one arm said to resemble Alfred Coverley, son of the first owners, still prowls the ruin, according to a plaque at the side.
"You will get a call from certain gentlemen … And they will say, 'Look, you know, we want to continue to have contracts with you … there is an honours system as you know', all this kind of thing.
Wintour told Fawkes that "some good frends of his wished his company in Ingland", and that certain gentlemen "were uppon a resolution to doe some whatt in Ingland if the pece with Spain healped us nott".
I declined the invitation, preferring silence and a stiffer sentence to the displeasure of certain gentlemen I might have had to mention in my conversations with federal investigators.
