Roles can be marked as active/inactive through the Manage Roles task in Core.

As a Platform Manager: 
  1. Navigate to Core.
  2. Select Security > Roles
  3. Click on the role you want to make active/inactive.
  4. To the right of Role Properties, click Edit.
  5. Check the Active box to make the role Active, or un-check the Active box to make it Inactive.
  6. Click Save & Close.
User-added image

Note: A role must be Active to show in Role drop downs, such as through Core > Users > Edit User Profile Data, or Core > People Finder.