I need a SP2013 calendar with three main categories: Department, Events and Other. This part I can achieve by creating 3 calendars and using overlays to combine them into a single view. But then I need subcategories of John, Hayley, Mary and Victor for each of the 3 main categories so if I create a calendar entry for Events for example, I can associate John and Hayley to the entry. How can I then create a view for each of the subcategories e.g. a view for John that shows all items where John is associated for Department, Events and Other?
I would suppose to create calendar views like john_department, john_events, john_others. The Filter of this views is the field that assigned John and the main category, departement for example.
If you have created this 3 views for John you are able to overlay this 3 views to a Main category view for John. You are able to give every view a different colour in the overlay to differentiate the events or write the main category in the View Title.
You can either create 1 or 2 columns to add choice menus to "categorize" the data you have in the calendar. These columns can be filtered upon when you create calendar like views, you can use the AND option in the filter section to filter on multiple columns if need be. Finally you can add up to 10 overlays on one calendar styled view. Calendar overlays link to other calendar like views even if they exist on the same calendar.
If your users need to see items with their names depending on who is logged in it might be in your best interest to use the "people and groups" column type to add their names and you can then leverage the [Me] filter so depending on who is logged in they will see items where they are tagged.
It might be worthwhile to make a test list to get your concept out and then when you have it figured out you can apply what you have learned to the calendar that is currently in use.