In a family with parents who do not have hemophilia one son has hemophilia. Who was the carrier of the gene for hemophilia?

First of all, Spontaneous mutations account for 1/3 of the cases of genetic hemophilia. This means that 1 out of 3 people born with hemophilia have no family history of the trait prior to that person. In the scenario you are describing, you are assuming that there was a carrier when in fact, there is a good chance that there was not.

There is also a chance that the child born with hemophilia received the mutation from his mother. Frequently women will have the mutation on one X chromosome but not their second. Depending od the individual case, the mother could carry the gene but not be symptomatic.

It is impossible for the son to have received the gene from his father. Since in order for a boy to actually be a boy, he must receive his father's Y chromosome and not his X chromosome, a son cannot receive the affected X chromosome from his father. Also, in order for a father to pass the trait on through daughters, the father himself would be a hemophiliac.