The Old Catholic Church is a group of people who left the Catholic Church after the First Vatican Council. They, as indicated in the answer below, are no longer Catholic as they are not under the Holy Father. There is no "Roman Catholic Church, it's just Catholic, not Roman Catholic. Roman is an epithet first commonly used in England after the protestant revolt to describe the Catholic Church. It is never used by the official Catholic Church.

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Once you split from the leadership of the pope, you cease to be Catholic. Members of the Old Catholic Church are Catholic in name only.