What is the ruling on an 'Umrah performed on behalf of a deceased father, given that the performer had previously performed Hajj but never 'Umrah?

If you perform Umrah on behalf of your father before performing it for yourself, then the Umrah for your father is not valid. This is because performing Umrah on behalf of another is not valid unless a person has first performed Umrah for himself. This has been established from the Prophet, peace and blessings be upon him, concerning Hajj, and Umrah is like Hajj in this regard. In this case, your Umrah will be for yourself, counting as the obligatory Umrah due upon you by Islam. This is the view of the Shafi'is and those who agree with them.