Fan Casting Middle Name Basis in Sort by Tropes

A character prefers to go by their middle name rather than their first name. The reasons for this can vary. Maybe they want to hide their identity and use their Real Name as an Alias or they just want a Meaningful Rename but is much easier to legally go by your middle name than fully changing it to a new one. Or maybe they want to differentiate themselves from a person sharing their name, which is especially common among children named after their parents (especially the father), who may go on this name basis because they don't like being called "Junior".