A fixer (not the kind used in photography) is a negotiator, intermediary, liaison etc.

Thank you very much, Kippesoep! 😎

Pssst, don't tell anybody, but I've heard that you can search for "Gran diccionario oxford 3ª ed 2003" in a popular program represented by a hybrid between a horse and a donkey 😉

Thank you all.

I have got another doubt/question.

What is the exact meaning of "guilty as charged"? It seems to be a very common phrase.

When a person is "charged with" something, it means criminal charges have been brought against him for breaking the law (i.e. he will be prosecuted in court). To say that somebody is "guilty as charged" means that those charges were correct and that that person was indeed guilty of committing those crimes, "as charged".

It can also be used a bit more lightly, such as the following:
Q: Are you the guy who played the piano in the school auditorium yesterday?
A: Guilty as charged.

In this case, it simply means "yes' 😀

Thank you very much! 😎

As Kippesoep explained, the colloquial usage of the phrase "guilty as charged" is as a semi-humorous affirmative response to an accusation.

The originating usage (I think) is in court proceedings, in which a judge proclaims that the jury has convicted the accused of the crimes with which (s)he was charged.

Also, I've never heard the term "political fixer" before.