This service, kindly made available by the GTS Group, you can find free and quickly who is the owner of a domain name
How does the whois work ?
All owners of different name present on Internet domains are subject to rigorous legislation, which requires the ability to identify them in case of legal problem. International law thus requires all registars, that is to say to companies that register domain names, to make the details of their customers and integrate them into a database called Whois. The Whois database is public and allows anyone to find the owner of a domain name from it.

You should know that the Whois database is spread across multiple servers based on the extension of the domain (.fr, .com, .org, .net, etc …). So there is a database for sites in .com, .net one for another for .fr. The Whois database for .fr domains managed by AFNIC, the French Association for Internet Names and Cooperation (semi-state institution).

All they own identifiable from the Whois?
Some domains name owners may decide to hide their whois data. That does not mean they are not present in the database, but the data are not made public: only the legal and judicial institutions can access it. This service therefore will display only public data.