Description and purpose of standard system user accounts in Red Hat Enterprise Linux

Issue

• Where can one find a short description of all the standard system users?
• Where can I find information about following system user accounts: shutdown, reboot, halt, sync, uucp, ftp, gopher, games, pcap (used by tcpdump)
• Where to find list of system (standard) uid(s)/gid(s)
• List of default system accounts
• Which are the priviledged user/group accounts in Red Hat Enterprise Linux ?
• What is purpose of system accounts ? i.e: (user accounts having a UID less than 500 for RHEL 6 and below and less than 1000 for RHEL 7 and above)
• Is it possible to remove/delete/disable default (standard) system user(s) accounts from Red Hat Enterprise Linux ?
• How to disable/reassign UID for system user accounts