Who's This? The private eye on page 1 of Who's Who vol.XXIV.
How you could have heard of him: On Week 18 of the 52 series, Tim Trench was killed and revealed to be a member of the same detective secret society the Dibnies, Detective Chimp and Traci Thirteen were in. So his 8th ever appearance was as a mystery to be solved...
Example story: Detective Comics #461 (1976) by Denny O'Neil, Pablo Marcos and Al Milgrom
Oh man, now I wish this strip had run a lot longer. O'Neil would bring the same kind of grit to other projects, of course, perhaps most notably his work on the Question and various pulp properties, even his Daredevil, but never with this much film noir flair. I would like to imagine Trench's modern stories, where he is basically a man out of time, playing at being a film noir hero, putting on those speech patterns, and perhaps really being as mad as any Batman villain, though on the side of the angels. Bored to Death without the stoner comedy?
Who else? Place your bets! Volume XXIV of Who's Who probably has 7 or 8 more entries that could fit the bill!