Deneuve

Deneuve (ドヌーヴ, Donūvu) is the name of the third most famous detective in the world. From the beginning of the series, the actual Deneuve isn't present; L has used their name as an alias in numerous cases.

Plot
L tells the Task Force that he uses Eraldo Coil as well as Deneuve as aliases with the purpose of further concealing his identity, considering anyone looking to investigate him is likely to contact either of them, as they are the second and third most well-known detectives, respectively.

In other media
In Death Note: Another Note: The Los Angeles BB Murder Cases, it is revealed that Deneuve was, in fact, a real person before giving up their name to L when L won a detective war between L, Deneuve, and Coil. In the very same book, it is also stated that it is common knowledge, for the most part, that the three are the same person.