Does anyone know If a writer wants to use as his character in a fiction the name Doctor Sigmund Freud is?

You may use Freud as a character, however that story has already been done. I don't recall the name, but I have read a story where Freud tries to catch the Ripper. Pax- C

A person's name cannot be copyrighted. It can in some cases be trademarked, but that usually applies to merchandise (like sports jerseys) rather than the use of a person's name in print.

A copyright only applies to artistic or intellectual work. Freud's writings or photos of Freud could still be under copyright, but not the man himself or his name. If you want to quote from Freud's writings note that anything Freud published before 1923 is now in the public domain, but that applies only to the original text. A more recent English translation could be under the copyright of the translator.

If Freud were still alive, you might have to worry about possible libel or invasion of privacy charges if you used him in a fictional story. But public figures are considered to have less of a right to privacy than regular people, and dead people are not considered to have any right to privacy at all. So you can write just about anything you want about Freud. He's been used as a character in other works of fiction, like "The Seven Percent Solution" where he psychoanalyzes Sherlock Holmes.

You can, but it's been done before.