Unless you live in a country that proscribes names that you can register a child with you are at liberty to call them what you want. Even if you can't register the name, you can still call them that informally. For example my daughters middle name is registered as squidge. There is a man in my parents home town that's named Portsmouth football club
A person is given a name by his or her parents, or guardian. They use names used before by the family, or ones they have heard and like. Pops can be used but it is usually only used as a name of endearment.